Dead Sea: a saltwater lake on the border between Israel and Jordan; its surface in 1292 feet below sea level


deep: literary term for an ocean


defile: a narrow pass (especially one between mountains)


gorge: a narrow pass (especially one between mountains)


Deimos: the outer of two small satellites of Mars


Delaware: a river that rises in the Catskills in southeastern New York and flows southward along the border of Pennsylvania with New York and New Jersey to northern Delaware where it empties into Delaware Bay


Delaware River: a river that rises in the Catskills in southeastern New York and flows southward along the border of Pennsylvania with New York and New Jersey to northern Delaware where it empties into Delaware Bay


Delaware Bay: an inlet of the North Atlantic; fed by the Delaware River


dell: a small wooded hollow


dingle: a small wooded hollow


Delphinus: a constellation in the northern hemisphere near Pegasus and Aquila


delta: a low triangular area of alluvial deposits where a river divides before entering a larger body of water


delta ray: an electron ejected from matter by ionizing radiation


Demerara: a river in northern Guyana that flows northward into the Atlantic


Denali Fault: a major open geological fault in Alaska


Deneb: the brightest star in Cygnus


Denebola: a star in Leo approximately 43 light years from Earth


descent: a downward slope or bend


declivity: a downward slope or bend


fall: a downward slope or bend


decline: a downward slope or bend


declination: a downward slope or bend


declension: a downward slope or bend


downslope: a downward slope or bend


desideratum: something desired as a necessity


Detroit River: a short river flowing from Lake St. Clair to Lake Erie along the border between the United States and Canada; one the busiest inland waterways in the world


deuteron: the nucleus of deuterium; consists of one proton and one neutron; used as a bombarding particle in accelerators


Dhaulagiri: a mountain in the Himalayas in Nepal (26,820 feet high)


diapir: a domed rock formation where a core of rock has moved upward and pierced through the more brittle overlying strata


diffuse nebula: a cluster of stars within an intricate cloud of gas and dust


gaseous nebula: a cluster of stars within an intricate cloud of gas and dust


dipole: a pair of equal and opposite electric charges or magnetic poles separated by a small distance


dipole molecule: a molecule that is a permanent dipole


direct transmission: a transmission mechanism in which the infectious agent is transferred directly into the body via touching or biting or kissing or sexual intercourse or by droplets entering the eye or nose or mouth


discard: anything that is cast aside or discarded


distributary: a branch of a river that flows away from the main stream and does not rejoin it


ditch: any small natural waterway


divot: a piece of turf dug out of a lawn or fairway (by an animals hooves or a golf club)


divot: (golf) the cavity left when a piece of turf is cut from the ground by the club head in making a stroke


Dnieper: a river that rises in Russia near Smolensk and flowing south through Belarus and Ukraine to empty into the Black Sea


Dnieper River: a river that rises in Russia near Smolensk and flowing south through Belarus and Ukraine to empty into the Black Sea


dog shit: fecal droppings from a dog


dog do: fecal droppings from a dog


doggy do: fecal droppings from a dog


dog turd: fecal droppings from a dog


Dolomite Alps: an eastern range of the Alps in northeastern Italy famous for their dolomitic limestone


Don: a European river in southwestern Russia; flows into the Sea of Azov


Don River: a European river in southwestern Russia; flows into the Sea of Azov


Donner Pass: a mountain pass in northeastern California near Lake Tahoe; site where in 1844 some members of an emigrant party survived by eating those who had died


Dorado: a constellation in the southern hemisphere near Reticulum and Pictor; contains most of the Large Magellanic Cloud


down: (usually plural) a rolling treeless highland with little soil


downhill: the downward slope of a hill


down quark: a stable quark with an electric charge of -1/3 and a mass 607 times that of an electron


Draco: a faint constellation twisting around the north celestial pole and lying between Ursa Major and Cepheus


Dragon: a faint constellation twisting around the north celestial pole and lying between Ursa Major and Cepheus


draw: a gully that is shallower than a ravine


dregs: sediment that has settled at the bottom of a liquid


settlings: sediment that has settled at the bottom of a liquid


drey: the nest of a squirrel


drift: a large mass of material that is heaped up by the wind or by water currents


drift ice: masses of ice floating in the open sea


drink: any large deep body of water


drumlin: a mound of glacial drift


dune: a ridge of sand created by the wind; found in deserts or near lakes and oceans


sand dune: a ridge of sand created by the wind; found in deserts or near lakes and oceans


Earth: the 3rd planet from the sun; the planet we live on


earth: the 3rd planet from the sun; the planet we live on


world: the 3rd planet from the sun; the planet we live on


globe: the 3rd planet from the sun; the planet we live on


East China Sea: part of the Pacific Ocean near eastern Asia


Ebro: a river in northeastern Spain; flows into the Mediterranean


Ebro River: a river in northeastern Spain; flows into the Mediterranean


Elbe: a river in central Europe that arises in northwestern Czechoslovakia and flows northward through Germany to empty into the North Sea


Elbe River: a river in central Europe that arises in northwestern Czechoslovakia and flows northward through Germany to empty into the North Sea


electric dipole: a dipole with equal and opposite electric charges


electric doublet: a dipole with equal and opposite electric charges


electron: an elementary particle with negative charge


negatron: an elementary particle with negative charge


elementary particle: (physics) a particle that is less complex than an atom; regarded as constituents of all matter


fundamental particle: (physics) a particle that is less complex than an atom; regarded as constituents of all matter


eliminator: an agent that eliminates something


Elizabeth River: a short river in southeastern Virginia flowing between Norfolk and Portsmouth into Hampton Roads


El Libertador: a mountain in the Andes in Argentina (22,047 feet high)


El Muerto: a mountain peak in the Andes on the border between Argentina and Chile (21,457 feet high)


ember: a hot fragment of wood or coal that is left from a fire and is glowing or smoldering


coal: a hot fragment of wood or coal that is left from a fire and is glowing or smoldering


enclosure: a naturally enclosed space


natural enclosure: a naturally enclosed space


English Channel: an arm of the Atlantic Ocean that forms a channel between France and Britain


enterolith: a calculus occurring in the intestines


envelope: a natural covering (as by a fluid)


Epsilon Aurigae: the largest known star


Eridanus: a constellation in the southern hemisphere near Fornax and Cetus


escarpment: a long steep slope or cliff at the edge of a plateau or ridge; usually formed by erosion


scarp: a long steep slope or cliff at the edge of a plateau or ridge; usually formed by erosion


esker: (geology) a long winding ridge of post glacial gravel and other sediment; deposited by meltwater from glaciers or ice sheets


estuary: the wide part of a river where it nears the sea; fresh and salt water mix


Euphrates: a river in southwestern Asia; flows into the Persian Gulf; was important in the development of several great civilizations in ancient Mesopotamia


Euphrates River: a river in southwestern Asia; flows into the Persian Gulf; was important in the development of several great civilizations in ancient Mesopotamia


Eurasia: the land mass formed by the continents of Europe and Asia


Europa: the 4th largest of Jupiter's satellites; covered with a smooth shell of frozen water


Europe: the 2nd smallest continent (actually a vast peninsula of Eurasia); the British use `Europe' to refer to all of the continent except the British Isles


evening star: a planet (usually Venus) seen at sunset in the western sky


Hesperus: a planet (usually Venus) seen at sunset in the western sky


Vesper: a planet (usually Venus) seen at sunset in the western sky


Everest: a mountain in the central Himalayas on the border of Tibet and Nepal; the highest mountain peak in the world (29,028 feet high)


Mount Everest: a mountain in the central Himalayas on the border of Tibet and Nepal; the highest mountain peak in the world (29,028 feet high)


Mt. Everest: a mountain in the central Himalayas on the border of Tibet and Nepal; the highest mountain peak in the world (29,028 feet high)


Everglades: a large subtropical swamp in southern Florida that is noted for its wildlife


exosphere: the outermost atmospheric layer


expanse: a wide and open space or area as of surface or land or sky


extraterrestrial object: a natural object existing outside the earth and outside the earth's atmosphere


estraterrestrial body: a natural object existing outside the earth and outside the earth's atmosphere


Eyre: a shallow salt lake in south central Australia about 35 feet below sea level; the largest lake in the country and the lowest point on the continent


Lake Eyre: a shallow salt lake in south central Australia about 35 feet below sea level; the largest lake in the country and the lowest point on the continent


Eyre Peninsula: a peninsula of southern Australia


fallow: cultivated land that is not seeded for one or more growing seasons


fatigue crack: a crack in metal resulting from metal fatigue


fault: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other


faulting: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other


geological fault: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other


shift: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other


fracture: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other


break: (geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other


feeder: a branch that flows into the main stream


tributary: a branch that flows into the main stream


confluent: a branch that flows into the main stream


affluent: a branch that flows into the main stream


fermion: any particle that obeys Fermi-Dirac statistics and is subject to the Pauli exclusion principle


filing: a fragment rubbed off by the use of a file


finding: something that is found


Fingal's Cave: a large cave with basaltic pillars on Staffa island in Scotland


fireball: the luminous center of a nuclear explosion


fireball: a ball of fire (such as the sun or a ball-shaped discharge of lightning)


fire pit: a pit whose floor is incandescent lava


firestone: a sandstone that withstands intense heat; used to line fireplaces and furnaces and kilns


firth: a long narrow estuary (especially in Scotland)


Firth of Clyde: a firth on the southwestern coast of Scotland emptying into the North Channel


Firth of Forth: a large firth on the east coast of Scotland and the estuary of the Forth River; location of Edinburgh


fishpond: a freshwater pond with fish


fixed star: any star in the Ptolemaic theory of planetary motion


fjord: a long narrow inlet of the sea between steep cliffs; common in Norway


fiord: a long narrow inlet of the sea between steep cliffs; common in Norway


flare star: a red dwarf star in which luminosity can change several magnitudes in a few minutes


flat: a level tract of land


Flint: a river in western Georgia that flows generally south to join the Chattahoochee River at the Florida border where they form the Apalachicola River


Flint River: a river in western Georgia that flows generally south to join the Chattahoochee River at the Florida border where they form the Apalachicola River


floater: an object that floats or is capable of floating


floodplain: a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding


flood plain: a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding


floor: the bottom surface of any lake or other body of water


floor: the ground on which people and animals move about


floor: the lower inside surface of any hollow structure


flowage: a body of water that has been created by deliberately flooding an area


foam: a mass of small bubbles formed in or on a liquid


froth: a mass of small bubbles formed in or on a liquid


folium: a thin layer or stratum of (especially metamorphic) rock


fomite: any inanimate object (as a towel or money or clothing or dishes or books or toys etc.) that can transmit infectious agents from one person to another


vehicle: any inanimate object (as a towel or money or clothing or dishes or books or toys etc.) that can transmit infectious agents from one person to another


foothill: a relatively low hill on the lower slope of a mountain


footwall: the lower wall of an inclined fault


ford: a shallow area in a stream that can be forded


crossing: a shallow area in a stream that can be forded


foreland: land forming the forward margin of something


foreshore: the part of the seashore between the highwater mark and the low-water mark


forest: land that is covered with trees and shrubs


woodland: land that is covered with trees and shrubs


timberland: land that is covered with trees and shrubs


timber: land that is covered with trees and shrubs


Fornax: a faint constellation in the southern hemisphere near Cetus and Phoenix


Forth: a river in southern Scotland that flows eastward to the Firth of Forth


Forth River: a river in southern Scotland that flows eastward to the Firth of Forth


fossil: the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil


Fountain of Youth: a fountain described in folk tales as able to make people young again


Fox River: a river in Wisconsin that flows into Lake Michigan


fragment: a piece broken off or cut off of something else


free electron: electron that is not attached to an atom or ion or molecule but is free to move under the influence of an electric field


Galan: a mountain peak in the Andes in Argentina (21,654 feet high)


Galilean satellite: one of the four satellites of Jupiter that were discovered by Galileo


Galilean: one of the four satellites of Jupiter that were discovered by Galileo


gallstone: a calculus formed in the gall bladder or its ducts


bilestone: a calculus formed in the gall bladder or its ducts


Galveston Bay: an arm of the Gulf of Mexico in Texas to the south of Houston


Galway Bay: a bay of the North Atlantic on the west coast of Ireland


Ganges: an Asian river; rises in the Himalayas and flows east into the Bay of Bengal; a sacred river of the Hindus


Ganges River: an Asian river; rises in the Himalayas and flows east into the Bay of Bengal; a sacred river of the Hindus


Gan Jiang: a river in southeastern China that flows generally north into the Chang Jiang to the north of Nanchang


Kan River: a river in southeastern China that flows generally north into the Chang Jiang to the north of Nanchang


Ganymede: the largest of Jupiter's satellites


Garonne: a river that rises in the Pyrenees and flows northwest to the Bay of Biscay


Garonne River: a river that rises in the Pyrenees and flows northwest to the Bay of Biscay


Gasherbrum: a mountain in northern Kashmir (26,470 feet high)


gauge boson: a particle that mediates the interaction of two elementary particles


Gemini: a zodiacal constellation in the northern hemisphere between Taurus and Cancer on the ecliptic


geode: (mineralogy) a hollow rock or nodule with the cavity usually lined with crystals


geological formation: (geology) the geological features of the earth


formation: (geology) the geological features of the earth


geyser: a spring that discharges hot water and steam


giant star: a very bright star of large diameter and low density (relative to the Sun)


giant: a very bright star of large diameter and low density (relative to the Sun)


Gila: a river that rises in western New Mexico and flows westward through southern Arizona to become a tributary of the Colorado River


Gila River: a river that rises in western New Mexico and flows westward through southern Arizona to become a tributary of the Colorado River


glacial boulder: a boulder that has been carried by a glacier to a place far distant from its place of origin


glacier: a slowly moving mass of ice


glen: a narrow secluded valley (in the mountains)


globule: a small globe or ball


gluon: a gauge boson that mediates strong interaction among quarks


Golden Gate: a strait in western California that connects the San Francisco Bay with the Pacific Ocean; discovered in 1579 by Sir Francis Drake


Gondwanaland: a hypothetical continent that (according to plate tectonic theory) broke up later into India and Australia and Africa and South America and Antarctica


gopher hole: a hole in the ground made by gophers


gorge: a deep ravine (usually with a river running through it)


Gosainthan: a mountain in the Himalayas in Tibet (26,290 feet high)


grain: a relatively small granular particle of a substance


Grand Canyon: the enormous gorge of the Colorado River in northern Arizona


Grand River: a river in southern Michigan that flows northwest to empty into Lake Michigan


Grand Teton: a mountain peak in northwestern Wyoming; the highest peak in the Teton Range (13,766 feet high)


granule: a tiny grain


graviton: a gauge boson that mediates the (extremely weak) gravitational interactions between particles


Great Attractor: a massive grouping of galaxies in the direction of Centaurus and Hydra whose gravitational attraction is believed to cause deviations in the paths of other galaxies


Great Australian Bight: a wide bay of the Indian Ocean in southern Australia; notorious for storms


Great Bear: a constellation outside the zodiac that rotates around the North Star


Ursa Major: a constellation outside the zodiac that rotates around the North Star


Great Barrier Reef: the largest coral reef in the world; in the Coral Sea off the northeastern coast of Australia


Great Dividing Range: a mountain range running along the eastern coast of Australia


Eastern Highlands: a mountain range running along the eastern coast of Australia


Great Lakes: a group of five large, interconnected lakes in central North America


Great Plains: a vast prairie region extending from Alberta and Saskatchewan and Manitoba in Canada south through the west central United States into Texas; formerly inhabited by Native Americans


Great Plains of North America: a vast prairie region extending from Alberta and Saskatchewan and Manitoba in Canada south through the west central United States into Texas; formerly inhabited by Native Americans


Great Rift Valley: ( geology) a depression in southwestern Asia and eastern Africa; extends from the valley of the Jordan River to Mozambique; marked by geological faults


Great Salt Lake: a shallow body of salt water in northwestern Utah


Great Slave Lake: a lake in the Northwest Territories in northwestern Canada; drained by the Mackenzie River


Great Smoky Mountains: part of the Appalachians between North Carolina and Tennessee


Green: a river that rises in western Wyoming and flows southward through Utah to become a tributary of the Colorado River


Green River: a river that rises in western Wyoming and flows southward through Utah to become a tributary of the Colorado River


Greenland Sea: part of the Arctic Ocean to the north of Iceland


Green Mountains: a range of the Appalachian Mountains that extends from south to north through Vermont


greenwood: woodlands in full leaf


grinding: material resulting from the process of grinding


grotto: a small cave (usually with attractive features)


grot: a small cave (usually with attractive features)


grounds: dregs consisting of solid particles (especially of coffee) that form a residue


growler: a small iceberg or ice floe just large enough to be hazardous for shipping


growth: something grown or growing


Grus: a small constellation in the southern hemisphere near Phoenix


Crane: a small constellation in the southern hemisphere near Phoenix


Guadalupe Mountains: a mountain range in southern New Mexico and western Texas; the southern extension of the Sacramento Mountains


Guantanamo Bay: an inlet of the Caribbean Sea; a United States naval station was established on the bay in 1903


gulch: a narrow gorge with a stream running through it


flume: a narrow gorge with a stream running through it


gulf: a deep wide chasm


gulf: an arm of a sea or ocean partly enclosed by land; larger than a bay


Gulf Coast: a seashore of the Gulf of Mexico


Gulf of Aden: arm of the Indian Ocean at the entrance to the Red Sea


Gulf of Alaska: a gulf of the Pacific Ocean between the Alaska Peninsula and the Alexander Archipelago


Gulf of Antalya: a gulf of the Mediterranean Sea in southwestern Turkey


Gulf of Aqaba: a northeastern arm of the Red Sea; between the Sinai Peninsula (Egypt) and Saudi Arabia


Gulf of Akaba: a northeastern arm of the Red Sea; between the Sinai Peninsula (Egypt) and Saudi Arabia


Gulf of Bothnia: a northern arm of the Baltic Sea; between Sweden and Finland


Gulf of California: a gulf to the west of the mainland of Mexico


Sea of Cortes: a gulf to the west of the mainland of Mexico


Gulf of Campeche: a part of the Gulf of Mexico to the west of Yucatan


Golfo de Campeche: a part of the Gulf of Mexico to the west of Yucatan


Bay of Campeche: a part of the Gulf of Mexico to the west of Yucatan


Gulf of Carpentaria: a wide shallow inlet of the Arafura Sea in northern Australia


Carpentaria: a wide shallow inlet of the Arafura Sea in northern Australia


Gulf of Corinth: inlet of the Ionian Sea between central Greece and the Peloponnesus


Gulf of Lepanto: inlet of the Ionian Sea between central Greece and the Peloponnesus


Gulf of Finland: an eastern arm of the Baltic Sea; between Finland and Estonia


Gulf of Guinea: a gulf off the southwest coast of Africa


Gulf of Martaban: an arm of the Andaman Sea off southern Myanmar


Gulf of Mexico: an arm of the Atlantic to the south of the United States and to the east of Mexico


Golfo de Mexico: an arm of the Atlantic to the south of the United States and to the east of Mexico


Gulf of Ob: an inlet of the Kara Sea in western Siberia


Bay of Ob: an inlet of the Kara Sea in western Siberia


Gulf of Oman: an arm of the Arabian Sea connecting it with the Persian Gulf


Gulf of Riga: an inlet of the Baltic Sea between Latvia and Estonia


Gulf of Saint Lawrence: an arm of the northwest Atlantic Ocean off the southeastern coast of Canada


Gulf of St. Lawrence: an arm of the northwest Atlantic Ocean off the southeastern coast of Canada


Gulf of Sidra: wide inlet of the Mediterranean Sea on the north coast of Libya


Gulf of Suez: a northwestern arm of the Red Sea linked to the Mediterranean by the Suez Canal


Gulf of Tehuantepec: an arm of the Pacific in southern Mexico


Gulf of Thailand: an arm of the South China Sea between Indochina and the Malay Peninsula


Gulf of Siam: an arm of the South China Sea between Indochina and the Malay Peninsula


Gulf of Venice: an arm of the Adriatic Sea


gully: deep ditch cut by running water (especially after a prolonged downpour)


gut: a narrow channel or strait


guyot: a seamount of volcanic origin (especially in the Pacific Ocean)


hadron: any elementary particle that interacts strongly with other particles


hail: many objects thrown forcefully through the air


hairball: a compact mass of hair that forms in the alimentary canal (especially in the stomach of animals as a result of licking fur)


hair ball: a compact mass of hair that forms in the alimentary canal (especially in the stomach of animals as a result of licking fur)


trichobezoar: a compact mass of hair that forms in the alimentary canal (especially in the stomach of animals as a result of licking fur)


Hampton Roads: a channel in southeastern Virginia through which the Elizabeth River and the James River flow into Chesapeake Bay


Handies Peak: a mountain peak in the San Juan Mountains in southwestern Colorado (14,048 feet high)


hanging wall: the upper wall of an inclined fault


Hangzhou Bay: a bay formed by an inlet of the East China Sea


head: the foam or froth that accumulates at the top when you pour an effervescent liquid into a container


head: a rounded compact mass


headstream: a stream that forms the source of a river


Hercules: a large constellation in the northern hemisphere between Lyra and Corona Borealis


heterocyclic ring: a ring of atoms of more than one kind; especially a ring of carbon atoms containing at least one atom that is not carbon


heterocycle: a ring of atoms of more than one kind; especially a ring of carbon atoms containing at least one atom that is not carbon


highland: elevated (e.g., mountainous) land


upland: elevated (e.g., mountainous) land


high sea: the open seas of the world outside the territorial waters of any nation


international waters: the open seas of the world outside the territorial waters of any nation


hill: a local and well-defined elevation of the land


hillside: the side or slope of a hill


Himalayas: a mountain range extending 1500 miles on the border between India and Tibet; this range contains the world's highest mountain


Himalaya Mountains: a mountain range extending 1500 miles on the border between India and Tibet; this range contains the world's highest mountain


Himalaya: a mountain range extending 1500 miles on the border between India and Tibet; this range contains the world's highest mountain


Hindu Kush: a mountain range extending to the west of the Himalayas


Hindu Kush Mountains: a mountain range extending to the west of the Himalayas


hogback: a narrow ridge of hills


horseback: a narrow ridge of hills


hole: an opening into or through something


hole: a depression hollowed out of solid matter


hollow: a depression hollowed out of solid matter


hollow: a small valley between mountains


holler: a small valley between mountains


holystone: a soft sandstone used for scrubbing the decks of a ship


hood: a protective covering that is part of a plant


cap: a protective covering that is part of a plant


Hook of Holland: a cape on the southwestern coast of the Netherlands near Rotterdam


Hoek van Holland: a cape on the southwestern coast of the Netherlands near Rotterdam


horsepond: a pond for watering horses


horst: a ridge of the earth's crust that has been forced upward between two faults and so is higher than the surrounding land


hot spring: a natural spring of water at a temperature of 70 F or above


thermal spring: a natural spring of water at a temperature of 70 F or above


Housatonic: a river that rises in western Massachusetts and flows south through Connecticut to empty into Long Island Sound


Housatonic River: a river that rises in western Massachusetts and flows south through Connecticut to empty into Long Island Sound


Huang He: a major river of Asia in northern China; flows generally eastward into the Yellow Sea; carries large quantities of yellow silt to its delta


Hwang Ho: a major river of Asia in northern China; flows generally eastward into the Yellow Sea; carries large quantities of yellow silt to its delta


Yellow River: a major river of Asia in northern China; flows generally eastward into the Yellow Sea; carries large quantities of yellow silt to its delta


Huascaran: a mountain in the Andes in Peru (22,205 feet high)


Hubbard: a mountain peak in southeastern Alaska that is part of the Coast Range (14,950 feet high)


Mount Hubbard: a mountain peak in southeastern Alaska that is part of the Coast Range (14,950 feet high)


Hudson: a New York river; flows southward into New York Bay; explored by Henry Hudson early in the 17th century


Hudson River: a New York river; flows southward into New York Bay; explored by Henry Hudson early in the 17th century


Hudson Bay: an inland sea in northern Canada


Humber: an estuary in central northeastern England formed by the Ouse River and the Trent River


hunk: a large piece of something without definite shape


lump: a large piece of something without definite shape


Hydra: a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer


Snake: a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer


hydrogen ion: a positively charged atom of hydrogen; that is to say, a normal hydrogen atomic nucleus


hydrosphere: the watery layer of the earth's surface; includes water vapor


Hydrus: a constellation in the southern hemisphere near the south celestial pole


hyperon: any baryon that is not a nucleon; unstable particle with mass greater than a neutron


ice: the frozen part of a body of water


iceberg: a large mass of ice floating at sea; usually broken off of a polar glacier


berg: a large mass of ice floating at sea; usually broken off of a polar glacier


icecap: a mass of ice and snow that permanently covers a large area of land (e.g., the polar regions or a mountain peak)


ice cap: a mass of ice and snow that permanently covers a large area of land (e.g., the polar regions or a mountain peak)


icefall: a steep part of a glacier resembling a frozen waterfall


ice field: a large flat mass of ice (larger than an ice floe) floating at sea


ice floe: a flat mass of ice (smaller than an ice field) floating at sea


floe: a flat mass of ice (smaller than an ice field) floating at sea


ice mass: a large mass of ice


Iguazu: a large waterfall on the border between Argentina and Brazil


Iguazu Falls: a large waterfall on the border between Argentina and Brazil


Iguassu: a large waterfall on the border between Argentina and Brazil


Iguassu Falls: a large waterfall on the border between Argentina and Brazil


Victoria Falls: a large waterfall on the border between Argentina and Brazil


IJssel: a river in the central Netherlands flowing north to the IJsselmeer


IJssel river: a river in the central Netherlands flowing north to the IJsselmeer


IJsselmeer: a shallow lake in northwestern Netherlands created in 1932 by building a dam across the entrance to the Zuider Zee


Illampu: a mountain peak in the Andes in Bolivia (20,870 feet high)


Illimani: a mountain peak in the Andes in Bolivia (21,201 feet high)


Illinois River: a river in Illinois that flows southwest to the Mississippi River


impairer: an agent that impairs


inclined fault: a geological fault in which one side is above the other


inclusion body: any small intracellular body found within another (characteristic of certain diseases)


cellular inclusion: any small intracellular body found within another (characteristic of certain diseases)


inclusion: any small intracellular body found within another (characteristic of certain diseases)


index fossil: a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found


guide fossil: a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found


Indian Ocean: the 3rd largest ocean; bounded by Africa on the west, Asia on the north, Australia on the east and merging with the Antarctic Ocean to the south


Indigirka: a river in far eastern Siberia that flows generally northward to the Arctic Ocean


Indigirka River: a river in far eastern Siberia that flows generally northward to the Arctic Ocean


indirect transmission: a transmission mechanism in which the infectious agent is transferred to the person by a fomite of vector


indumentum: a covering of fine hairs (or sometimes scales) as on a leaf or insect


indument: a covering of fine hairs (or sometimes scales) as on a leaf or insect


Indus: an Asian river that rises in Tibet and flows through northern India and then southwest through Kashmir and Pakistan to the Arabian Sea


Indus River: an Asian river that rises in Tibet and flows through northern India and then southwest through Kashmir and Pakistan to the Arabian Sea


Indus: a faint constellation in the southern hemisphere near Telescopium and Tucana


inessential: anything that is not essential


nonessential: anything that is not essential


infectious agent: an agent capable of producing infection


infective agent: an agent capable of producing infection


inferior planet: any of the planets whose orbit lies inside the earth's orbit


ingrowth: something that grows inward


Inland Passage: a naturally protected waterway from Seattle to Skagway in southeastern Alaska


Inside Passage: a naturally protected waterway from Seattle to Skagway in southeastern Alaska


Inland Sea: an arm of the Pacific Ocean in southern Japan; surrounded by the islands of Honshu and Shikoku and Kyushu and linked to the Sea of Japan by a narrow channel; the chief port is Hiroshima


inlet: an arm off of a larger body of water (often between rocky headlands)


recess: an arm off of a larger body of water (often between rocky headlands)


inside track: the inner side of a curved racecourse


intermediate vector boson: a gauge boson that mediates weak interactions between particles


interplanetary dust: microscopic particles in the interplanetary medium


interplanetary gas: a rarefied flow of gas and charged particles (plasma) that stream from the sun and form the solar wind


interplanetary medium: interplanetary space including forms of energy and gas and dust


interstellar medium: interstellar space including streams of protons moving from the stars


intrusion: rock produced by an intrusive process


Io: the closest of Jupiter's moons; has active volcanoes


ion: a particle that is electrically charged (positive or negative); an atom or molecule or group that has lost or gained one or more electrons


Ionian Sea: an arm of the Mediterranean Sea between western Greece and southern Italy


Irish Sea: an arm of the North Atlantic between Great Britain and Ireland


iron filing: a fragment of iron rubbed off by the use of a file


Irrawaddy: the main river of Myanmar rising in the north and flowing south through the length of Burma to empty into the Andaman Sea


Irrawaddy River: the main river of Myanmar rising in the north and flowing south through the length of Burma to empty into the Andaman Sea


Irtish: an Asian river that rises in the Altai Mountains in northern China and flows generally northwest to become a tributary of the Ob River


Irtish River: an Asian river that rises in the Altai Mountains in northern China and flows generally northwest to become a tributary of the Ob River


Irtysh: an Asian river that rises in the Altai Mountains in northern China and flows generally northwest to become a tributary of the Ob River


Irtysh River: an Asian river that rises in the Altai Mountains in northern China and flows generally northwest to become a tributary of the Ob River


Isere: a river in southeastern France; a tributary of the Rhone


Isere River: a river in southeastern France; a tributary of the Rhone


island: a land mass (smaller than a continent) that is surrounded by water


isle: a small island


islet: a small island


isthmus: a relatively narrow strip of land (with water on both sides) connecting two larger land areas


Isthmus of Corinth: a narrow isthmus between the Gulf of Corinth and the Saronic Gulf; a canal crosses the isthmus so that navigation is possible between the gulfs


Isthmus of Kra: a narrow isthmus linking the Malay Peninsula to the Asian mainland


Isthmus of Panama: the isthmus that connects Central America and South America; was formerly called the Isthmus of Darien


Isthmus of Darien: the isthmus that connects Central America and South America; was formerly called the Isthmus of Darien


Isthmus of Suez: the isthmus in northeastern Egypt that connects Africa and Asia


Isthmus of Tehuantepec: the narrowest part of southern Mexico is an isthmus between the Bay of Campeche on the north coast and the Gulf of Tehuantepec on the south coast


jag: a sharp projection on an edge or surface


James: a river that rises in North Dakota and flows southward across South Dakota to the Missouri


James River: a river that rises in North Dakota and flows southward across South Dakota to the Missouri


James: a river in Virginia that flows east into Chesapeake Bay at Hampton Roads


James River: a river in Virginia that flows east into Chesapeake Bay at Hampton Roads


James Bay: the southern extension of Hudson Bay in Canada between western Quebec and northeastern Ontario


Japan Trench: a depression in the floor of the Pacific Ocean to the northeast of Japan that reaches depths of 30,000 feet


Jebel Musa: a promontory in northern Morocco opposite the Rock of Gibraltar; one of the Pillars of Hercules


Abila: a promontory in northern Morocco opposite the Rock of Gibraltar; one of the Pillars of Hercules


Abyla: a promontory in northern Morocco opposite the Rock of Gibraltar; one of the Pillars of Hercules


Jordan: a river in Palestine that empties into the Dead Sea; John the Baptist baptized Jesus in the Jordan


Jordan River: a river in Palestine that empties into the Dead Sea; John the Baptist baptized Jesus in the Jordan


Jovian planet: any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature (like Jupiter)


gas giant: any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature (like Jupiter)


J particle: a neutral meson with a large mass


psi particle: a neutral meson with a large mass


Jupiter: the largest planet and the 5th from the sun; has many satellites and is one of the brightest objects in the night sky


K2: a mountain peak in the Karakoram Range in northern Kashmir; the 2nd highest peak in the world (28,250 feet high)


Godwin Austen: a mountain peak in the Karakoram Range in northern Kashmir; the 2nd highest peak in the world (28,250 feet high)


Mount Godwin Austen: a mountain peak in the Karakoram Range in northern Kashmir; the 2nd highest peak in the world (28,250 feet high)


Dapsang: a mountain peak in the Karakoram Range in northern Kashmir; the 2nd highest peak in the world (28,250 feet high)


Kamet: a mountain in the Himalayas in northern India (25,450 feet high)


Kanawha: a tributary of the Ohio River in West Virginia


Kanawha River: a tributary of the Ohio River in West Virginia


Kanchenjunga: a mountain the Himalayas on the border between Nepal and Tibet (28,208 feet high)


Mount Kanchenjunga: a mountain the Himalayas on the border between Nepal and Tibet (28,208 feet high)


Kanchanjanga: a mountain the Himalayas on the border between Nepal and Tibet (28,208 feet high)


Kinchinjunga: a mountain the Himalayas on the border between Nepal and Tibet (28,208 feet high)


Kansas: a river in northeastern Kansas; flows eastward to become a tributary of the Missouri River


Kansas River: a river in northeastern Kansas; flows eastward to become a tributary of the Missouri River


Kaw River: a river in northeastern Kansas; flows eastward to become a tributary of the Missouri River


kaon: an unstable meson produced as the result of a high-energy particle collision


kappa-meson: an unstable meson produced as the result of a high-energy particle collision


k-meson: an unstable meson produced as the result of a high-energy particle collision


K particle: an unstable meson produced as the result of a high-energy particle collision


Karakoram: a mountain range in northern Kashmir; an extension of the Hindu Kush; contains the 2nd highest peak


Karakoram Range: a mountain range in northern Kashmir; an extension of the Hindu Kush; contains the 2nd highest peak


Karakorum Range: a mountain range in northern Kashmir; an extension of the Hindu Kush; contains the 2nd highest peak


Mustagh: a mountain range in northern Kashmir; an extension of the Hindu Kush; contains the 2nd highest peak


Mustagh Range: a mountain range in northern Kashmir; an extension of the Hindu Kush; contains the 2nd highest peak


Kara Sea: part of the Arctic Ocean to the north of Siberia and to the east of the Barents Sea; icebound most of the year


Karelian Isthmus: the isthmus between the Gulf of Finland and Lake Ladoga that connects Finland and Russia


Kasai: a river of southwestern Africa that rises in central Angola and flows east and then north (forming part of the border between Angola and Congo) and continuing northwest through Congo to empty into the Congo River on the border between Congo and Republic of the Congo


Kasai River: a river of southwestern Africa that rises in central Angola and flows east and then north (forming part of the border between Angola and Congo) and continuing northwest through Congo to empty into the Congo River on the border between Congo and Republic of the Congo


River Kasai: a river of southwestern Africa that rises in central Angola and flows east and then north (forming part of the border between Angola and Congo) and continuing northwest through Congo to empty into the Congo River on the border between Congo and Republic of the Congo


Kattegatt: a strait of the North Sea between Jutland and Sweden; connects with the North Sea through the Skagerrak


kettle hole: (geology) a hollow (typically filled by a lake) that results from the melting of a mass of ice trapped in glacial deposits


kettle: (geology) a hollow (typically filled by a lake) that results from the melting of a mass of ice trapped in glacial deposits


Keuka Lake: a glacial lake in central New York; one of the Finger Lakes


Lake Keuka: a glacial lake in central New York; one of the Finger Lakes


key: a coral reef off the southern coast of Florida


cay: a coral reef off the southern coast of Florida


Florida key: a coral reef off the southern coast of Florida


Khyber Pass: a mountain pass of great strategic and commercial value in the Hindu Kush on the border between northern Pakistan and western Afghanistan; a route by which invaders entered India


kidney stone: a calculus formed in the kidney


urinary calculus: a calculus formed in the kidney


nephrolith: a calculus formed in the kidney


renal calculus: a calculus formed in the kidney


Kilimanjaro: the highest peak in Africa; located in northeastern Tanzania; 19,340 feet high


Mount Kilimanjaro: the highest peak in Africa; located in northeastern Tanzania; 19,340 feet high


Kissimmee: a river of central Florida that flows southward to Lake Okeechobee


Kissimmee River: a river of central Florida that flows southward to Lake Okeechobee


Kivu: a lake in the mountains of central Africa between Congo and Rwanda


Lake Kivu: a lake in the mountains of central Africa between Congo and Rwanda


Klamath: a river flowing southwest from Oregon through northern California to the Pacific Ocean


Klamath River: a river flowing southwest from Oregon through northern California to the Pacific Ocean


knoll: a small natural hill


mound: a small natural hill


hillock: a small natural hill


hummock: a small natural hill


hammock: a small natural hill


Kodiak: an island off southern Alaska in the Gulf of Alaska; site of the first European settlement in the area which was founded by the Russians in 1784


Kodiak Island: an island off southern Alaska in the Gulf of Alaska; site of the first European settlement in the area which was founded by the Russians in 1784


kopje: a small hill rising up from the African veld


koppie: a small hill rising up from the African veld


Korea Bay: an inlet of the Yellow Sea between the Liaodong Peninsula in China and western Korea


Korean Strait: a strait between Korea and Japan; connects the East China Sea and the Sea of Japan


Korea Strait: a strait between Korea and Japan; connects the East China Sea and the Sea of Japan


Kuiper belt: a disk-shaped region of minor planets outside the orbit of Neptune


Edgeworth-Kuiper belt: a disk-shaped region of minor planets outside the orbit of Neptune


Kuiper belt object: any of many minor planets in the Kuiper belt outside the orbit of Neptune at the edge of the solar system


KBO: any of many minor planets in the Kuiper belt outside the orbit of Neptune at the edge of the solar system


Kunlun: a mountain range in western China that extends eastward from the Indian border for 1000 miles


Kunlan Shan: a mountain range in western China that extends eastward from the Indian border for 1000 miles


Kunlun Mountains: a mountain range in western China that extends eastward from the Indian border for 1000 miles


Kuenlun: a mountain range in western China that extends eastward from the Indian border for 1000 miles


Kuenlun Mountains: a mountain range in western China that extends eastward from the Indian border for 1000 miles


Kura: a river in western Asia; rises in northeast Turkey and flows to the Caspian Sea


Kura River: a river in western Asia; rises in northeast Turkey and flows to the Caspian Sea


Labrador-Ungava Peninsula: a peninsular region of eastern Canada between Hudson Bay and the Labrador Sea; contains most of Quebec and the mainland part of Newfoundland and Labrador


Labrador Peninsula: a peninsular region of eastern Canada between Hudson Bay and the Labrador Sea; contains most of Quebec and the mainland part of Newfoundland and Labrador


Labrador Sea: an arm of the northern Atlantic between Labrador and southern Greenland


lagoon: a body of water cut off from a larger body by a reef of sand or coral


laguna: a body of water cut off from a larger body by a reef of sand or coral


lagune: a body of water cut off from a larger body by a reef of sand or coral


lake: a body of (usually fresh) water surrounded by land


Lake Albert: a shallow lake on the border between Uganda and Congo in the Great Rift Valley


Lake Albert Nyanza: a shallow lake on the border between Uganda and Congo in the Great Rift Valley


Mobuto Lake: a shallow lake on the border between Uganda and Congo in the Great Rift Valley


Lake Aral: a lake to the east of the Caspian Sea lying between Kazakhstan and Uzbekistan


Aral Sea: a lake to the east of the Caspian Sea lying between Kazakhstan and Uzbekistan


lake bed: the bottom of a lake


lake bottom: the bottom of a lake


Lake Chad: a lake in north central Africa; fed by the Shari river


Chad: a lake in north central Africa; fed by the Shari river


Lake Champlain: a lake in northeastern New York, northwestern Vermont and southern Quebec; site of many battles in the French and Indian War and in the American Revolution and in the War of 1812


Champlain: a lake in northeastern New York, northwestern Vermont and southern Quebec; site of many battles in the French and Indian War and in the American Revolution and in the War of 1812


Lake Edward: a lake in the Great Rift Valley between Congo and Uganda


Lake Erie: the 4th largest of the Great Lakes; it is linked to the Hudson River by the New York State Barge Canal


Erie: the 4th largest of the Great Lakes; it is linked to the Hudson River by the New York State Barge Canal


lakefront: land bordering a lake


Lake Geneva: a lake between southwestern Switzerland and France that is crossed from east to west by the Rhone


Lake Leman: a lake between southwestern Switzerland and France that is crossed from east to west by the Rhone


Lake Huron: the 2nd largest of the Great Lakes


Huron: the 2nd largest of the Great Lakes


Lake Ilmen: a lake in northwestern Russia; drains through the Volkhov River into Lake Ladoga


Ilmen: a lake in northwestern Russia; drains through the Volkhov River into Lake Ladoga


Lake Ladoga: a lake in northwestern Russia to the north of St. Petersburg; the largest lake in Europe; drains through the Neva River into the Gulf of Finland


Ladoga: a lake in northwestern Russia to the north of St. Petersburg; the largest lake in Europe; drains through the Neva River into the Gulf of Finland


Lake Michigan: the 3rd largest of the Great Lakes; the largest freshwater lake entirely within the United States borders


Michigan: the 3rd largest of the Great Lakes; the largest freshwater lake entirely within the United States borders


Lake Nasser: lake in Egypt formed by dams built on the Nile River at Aswan


Nasser: lake in Egypt formed by dams built on the Nile River at Aswan


Lake Nyasa: a long lake in southeastern Africa between Tanzania, Mozambique, and Malawi


Lake Malawi: a long lake in southeastern Africa between Tanzania, Mozambique, and Malawi


Lake Onega: lake in northwestern Russia near the border with Finland; second largest lake in Europe


Onega: lake in northwestern Russia near the border with Finland; second largest lake in Europe


Lake Ontario: the smallest of the Great Lakes


Ontario: the smallest of the Great Lakes


lakeside: the shore of a lake


lakeshore: the shore of a lake


Lake St. Clair: a lake between Ontario and Michigan; connected with Lake Huron and Lake Erie


Lake Saint Clair: a lake between Ontario and Michigan; connected with Lake Huron and Lake Erie


Lake Superior: the largest freshwater lake in the world; the deepest of the Great Lakes


Superior: the largest freshwater lake in the world; the deepest of the Great Lakes


Lake Tana: a lake in northern Ethiopia; the largest lake in Ethiopia and the source of the Blue Nile


Lake Tsana: a lake in northern Ethiopia; the largest lake in Ethiopia and the source of the Blue Nile


Lake Tanganyika: the longest lake in the world in central Africa between Tanzania and Congo in the Great Rift Valley


Tanganyika: the longest lake in the world in central Africa between Tanzania and Congo in the Great Rift Valley


Lake Urmia: a shallow saline lake in northwestern Iran between Tabriz and the western border of Turkey


Urmia: a shallow saline lake in northwestern Iran between Tabriz and the western border of Turkey


Daryacheh-ye Orumiyeh: a shallow saline lake in northwestern Iran between Tabriz and the western border of Turkey


Lake Vanern: a lake in southwestern Sweden; the largest lake in Sweden


Vanern: a lake in southwestern Sweden; the largest lake in Sweden


Lake Victoria: the largest lake in Africa and the 2nd largest fresh water lake in the world; a headwaters reservoir for the Nile River


Victoria Nyanza: the largest lake in Africa and the 2nd largest fresh water lake in the world; a headwaters reservoir for the Nile River


lambda particle: an electrically neutral baryon with isotopic spin 1


lambda hyperon: an electrically neutral baryon with isotopic spin 1


land: the solid part of the earth's surface


dry land: the solid part of the earth's surface


earth: the solid part of the earth's surface


ground: the solid part of the earth's surface


solid ground: the solid part of the earth's surface


terra firma: the solid part of the earth's surface


land: material in the top layer of the surface of the earth in which plants can grow (especially with reference to its quality or use)


ground: material in the top layer of the surface of the earth in which plants can grow (especially with reference to its quality or use)


soil: material in the top layer of the surface of the earth in which plants can grow (especially with reference to its quality or use)


landfall: the seacoast first sighted on a voyage (or flight over water)


landfill: a low area that has been filled in


landmass: a large continuous extent of land


land mass: a large continuous extent of land


Laptev Sea: part of the Arctic Ocean to the north of Siberia (between the Taimyr Peninsula and the New Siberian Islands) that is icebound most of the year


Large Magellanic Cloud: the larger of the two Magellanic Clouds visible from the southern hemisphere


Lascaux: a cave in southwestern France that contains Paleolithic paintings


lather: the foam resulting from excessive sweating (as on a horse)


Laudo: a mountain peak in the Andes in Argentina (20,997 feet high)


Laurasia: a hypothetical continent that (according to plate tectonic theory) broke up later into North America and Europe and Asia


leak: an accidental hole that allows something (fluid or light etc.) to enter or escape


ledge: a projecting ridge on a mountain or submerged under water


shelf: a projecting ridge on a mountain or submerged under water


lees: the sediment from fermentation of an alcoholic beverage


Lehigh River: a river in eastern Pennsylvania that flows southeast into the Delaware River


Lena: a Russian river in Siberia; flows northward into the Laptev Sea


Lena River: a Russian river in Siberia; flows northward into the Laptev Sea


Leo: a zodiacal constellation in northern hemisphere between Cancer and Virgo


lepton: an elementary particle that participates in weak interactions; has a baryon number of 0


Lepus: a constellation in the southern hemisphere near Orion and Columba


lethal agent: an agent capable of causing death


Lethe: (Greek mythology) a river in Hades; the souls of the dead had to drink from it, which made them forget all they had done and suffered when they were alive


River Lethe: (Greek mythology) a river in Hades; the souls of the dead had to drink from it, which made them forget all they had done and suffered when they were alive


Lhotse: a mountain in the central Himalayas on the border of Tibet and Nepal (27,890 feet high)


Liaodong Peninsula: a peninsula in northeastern China that extends into the Yellow Sea, between Bo Hai and Korea Bay


Liaodong Bandao: a peninsula in northeastern China that extends into the Yellow Sea, between Bo Hai and Korea Bay


Libra: a small faint zodiacal constellation in the southern hemisphere; between Virgo and Scorpius


Ligurian Sea: an arm of the Mediterranean between northwest Italy and Corsica


liman: a long narrow lagoon near the mouth of a river


Limpopo: an African river; flows into the Indian Ocean


Crocodile River: an African river; flows into the Indian Ocean


liposomal delivery vector: a transducing vector that uses liposomes to carry the gene of interest


lithosphere: the solid part of the earth consisting of the crust and outer mantle


geosphere: the solid part of the earth consisting of the crust and outer mantle


Little Bear: a constellation outside the zodiac that rotates around the North Star


Ursa Minor: a constellation outside the zodiac that rotates around the North Star


Little Bighorn: a river that flows from northern Wyoming into the Bighorn River in southern Montana; site of Custer's Last Stand


Little Bighorn River: a river that flows from northern Wyoming into the Bighorn River in southern Montana; site of Custer's Last Stand


Little Horn: a river that flows from northern Wyoming into the Bighorn River in southern Montana; site of Custer's Last Stand


Little Dipper: a cluster of seven stars in Ursa Minor; at the end of the dipper's handle is Polaris


Dipper: a cluster of seven stars in Ursa Minor; at the end of the dipper's handle is Polaris


Little Missouri: a river that rises in northeastern Wyoming and flows through Montana and South Dakota to join the Missouri River in North Dakota


Little Missouri River: a river that rises in northeastern Wyoming and flows through Montana and South Dakota to join the Missouri River in North Dakota


Little Sioux River: a river that rises in southwestern Minnesota and flows southwestward to the Missouri River in western Iowa


Little Wabash: a river in eastern Illinois that flows southeastward to the Wabash River


Little Wabash River: a river in eastern Illinois that flows southeastward to the Wabash River


llano: an extensive grassy and nearly treeless plain (especially in Latin America)


Llano Estacado: a large semiarid plateau forming the southern part of the Great Plains


Llullaillaco: a mountain in the Andes on the border between Argentina and Chile (22,057 feet high)


loch: Scottish word for a lake


loch: a long narrow inlet of the sea in Scotland (especially when it is nearly landlocked)


Loch Achray: a lake in central Scotland


Loch Linnhe: an inlet of the Atlantic Ocean on the western coast of Scotland


Loch Ness: a lake in the Scottish highlands; the largest body of fresh water in Great Britain


lodestar: guiding star; a star that is used as a reference point in navigation or astronomy


loadstar: guiding star; a star that is used as a reference point in navigation or astronomy


Logan: a mountain peak in the St. Elias Range in the southwestern Yukon Territory in Canada (19,850 feet high)


Mount Logan: a mountain peak in the St. Elias Range in the southwestern Yukon Territory in Canada (19,850 feet high)


Loire: the longest French river; rises in the Massif Central and flows north and west to the Atlantic Ocean


Loire River: the longest French river; rises in the Massif Central and flows north and west to the Atlantic Ocean


Loire Valley: the valley of the Loire River where many French wines originated


long chain: (chemistry) a relatively long chain of atoms in a molecule


long-chain molecule: (chemistry) a relatively long chain of atoms in a molecule


Long Island Sound: a sound between Long Island and Connecticut


lough: Irish word for a lake


lough: a long narrow (nearly landlocked) cove in Ireland


Lower California: a mountainous peninsula on northwest Mexico


Baja California: a mountainous peninsula on northwest Mexico


lower mantle: the deeper part of the mantle


Lower Peninsula: the part of northern Michigan between Lake Michigan and Lake Huron


lowland: low level country


lunar crater: a crater on the Earth's Moon


Lupus: a constellation in the southern hemisphere near Centaurus


Lyra: a small constellation in the northern hemisphere near Cygnus and Draco; contains the star Vega


maar: a flat-bottomed volcanic crater that was formed by an explosion; often filled with water


Mackenzie: a Canadian river; flows into the Beaufort Sea


Mackenzie River: a Canadian river; flows into the Beaufort Sea


mackerel sky: a sky filled with rows of cirrocumulus or small altocumulus clouds


Madeira: a Brazilian river; tributary of the Amazon River


Madeira River: a Brazilian river; tributary of the Amazon River


Magdalena: a river that rises in the Andes mountains in southwestern Colombia and flows generally northward to empty into the Caribbean Sea at Barranquilla


Magdalena River: a river that rises in the Andes mountains in southwestern Colombia and flows generally northward to empty into the Caribbean Sea at Barranquilla


Magellanic Cloud: either of two small galaxies orbiting the Milky Way; visible near the south celestial pole


magnetic dipole: a dipole with opposing magnetic poles


magnetic monopole: a hypothetical particle with a single magnetic pole instead of the usual two


main: any very large body of (salt) water


briny: any very large body of (salt) water


mainland: the main land mass of a country or continent; as distinguished from an island or peninsula


Makalu: a mountain in the Himalayas in Nepal (27,790 feet high)


mantle: the layer of the earth between the crust and the core


mare: a dark region of considerable extent on the surface of the moon


maria: a dark region of considerable extent on the surface of the moon


mare clausum: (closed sea) a navigable body of water under the jurisdiction of a single nation


mare liberum: (free sea) a navigable body of water to which all nations have equal access


mare nostrum: (our sea) the Mediterranean to the ancient Romans


mare's tail: a long narrow flowing cirrus cloud


Marmara: an inland sea in northwestern Turkey; linked to the Black Sea by the Bosporus and linked to the Aegean by the Dardanelles


Sea of Marmara: an inland sea in northwestern Turkey; linked to the Black Sea by the Bosporus and linked to the Aegean by the Dardanelles


Marmara Denizi: an inland sea in northwestern Turkey; linked to the Black Sea by the Bosporus and linked to the Aegean by the Dardanelles


Marmora: an inland sea in northwestern Turkey; linked to the Black Sea by the Bosporus and linked to the Aegean by the Dardanelles


Sea of Marmora: an inland sea in northwestern Turkey; linked to the Black Sea by the Bosporus and linked to the Aegean by the Dardanelles


Mars: a small reddish planet that is the 4th from the sun and is periodically visible to the naked eye; minerals rich in iron cover its surface and are responsible for its characteristic color


Red Planet: a small reddish planet that is the 4th from the sun and is periodically visible to the naked eye; minerals rich in iron cover its surface and are responsible for its characteristic color


marsh: low-lying wet land with grassy vegetation; usually is a transition zone between land and water


marshland: low-lying wet land with grassy vegetation; usually is a transition zone between land and water


fen: low-lying wet land with grassy vegetation; usually is a transition zone between land and water


fenland: low-lying wet land with grassy vegetation; usually is a transition zone between land and water


mass: a body of matter without definite shape


Massachusetts Bay: an inlet of the Atlantic Ocean off of eastern Massachusetts extending from Cape Ann on the north to Cape Cod on the south


massif: a block of the earth's crust bounded by faults and shifted to form peaks of a mountain range


Massif Central: a mountainous plateau in southern France that covers almost one sixth of the country


mat: a mass that is densely tangled or interwoven


matchwood: fragments of wood


matrix: an enclosure within which something originates or develops (from the Latin for womb)


Matterhorn: a mountain in the Alps on the border between Switzerland and Italy (14,780 feet high); noted for its distinctive shape


McKinley: a mountain in south central Alaska; the highest peak in North America (20,300 feet high)


Mount McKinley: a mountain in south central Alaska; the highest peak in North America (20,300 feet high)


Mt. McKinley: a mountain in south central Alaska; the highest peak in North America (20,300 feet high)


Denali: a mountain in south central Alaska; the highest peak in North America (20,300 feet high)


meander: a bend or curve, as in a stream or river


mechanism: a natural object resembling a machine in structure or function


Mediterranean: the largest inland sea; between Europe and Africa and Asia


Mediterranean Sea: the largest inland sea; between Europe and Africa and Asia


Mekong: an Asian river; flows through a large delta in southern Vietnam into the South China Sea


Mekong River: an Asian river; flows through a large delta in southern Vietnam into the South China Sea


Menai Strait: a strait in northern Wales between Anglesey Island and the mainland


Mendenhall Glacier: a glacier of the Piedmont type near Juneau in Alaska


Great Mendenhall Glacier: a glacier of the Piedmont type near Juneau in Alaska


Mensa: a faint constellation in the polar region of the southern hemisphere and containing part of the Large Magellanic Cloud


Mercedario: a mountain in the Andes in Argentina (22,210 feet high)


Mercury: the smallest planet and the nearest to the sun


mere: a small pond of standing water


Merrimack: a river that rises in south central New Hampshire and flows through Concord and Manchester into Massachusetts and empties into the Atlantic Ocean


Merrimack River: a river that rises in south central New Hampshire and flows through Concord and Manchester into Massachusetts and empties into the Atlantic Ocean


mesa: flat tableland with steep edges


table: flat tableland with steep edges


Mesabi Range: a range of hills in northeastern Minnesota where rich iron ore deposits were discovered in 1887


meson: an elementary particle responsible for the forces in the atomic nucleus; a hadron with a baryon number of 0


mesotron: an elementary particle responsible for the forces in the atomic nucleus; a hadron with a baryon number of 0


mesosphere: the atmospheric layer between the stratosphere and the thermosphere


metal filing: a fragment of metal rubbed off by the use of a file


meteorite: stony or metallic object that is the remains of a meteoroid that has reached the earth's surface


meteoroid: (astronomy) any of the small solid extraterrestrial bodies that hits the earth's atmosphere


meteor: (astronomy) any of the small solid extraterrestrial bodies that hits the earth's atmosphere


meteor swarm: a group of meteoroids with similar paths


Meuse: a European river; flows into the North Sea


Meuse River: a European river; flows into the North Sea


micelle: an electrically charged particle built up from polymeric molecules or ions and occurring in certain colloidal electrolytic solutions like soaps and detergents


microfossil: a fossil that must be studied microscopically


micrometeorite: a meteorite or meteoroid so small that it drifts down to earth without becoming intensely heated in the atmosphere


micrometeoroid: a meteorite or meteoroid so small that it drifts down to earth without becoming intensely heated in the atmosphere


micrometeor: a meteorite or meteoroid so small that it drifts down to earth without becoming intensely heated in the atmosphere


Microscopium: a faint constellation in the southern hemisphere near Sagittarius and Capricornus


Mid-Atlantic Ridge: a very long narrow elevation on the ocean floor that runs all the way from Iceland in the North Atlantic to Bouvet Island in the South Atlantic


midstream: the middle of a stream


mid-water: the water that is well below the surface but also well above the bottom


Milk: a river that rises in the Rockies in northwestern Montana and flows eastward to become a tributary of the Missouri River


Milk River: a river that rises in the Rockies in northwestern Montana and flows eastward to become a tributary of the Missouri River


Milky Way: the galaxy containing the solar system; consists of millions of stars that can be seen as a diffuse band of light stretching across the night sky


Milky Way Galaxy: the galaxy containing the solar system; consists of millions of stars that can be seen as a diffuse band of light stretching across the night sky


Milky Way System: the galaxy containing the solar system; consists of millions of stars that can be seen as a diffuse band of light stretching across the night sky


millpond: a pond formed by damming a stream to provide a head of water to turn a mill wheel


Minamata Bay: a bay on the west coast of Kyushu; in the 1950s industrial wastes caused mercury poisoning among the Japanese people who ate fish from Minamata Bay


minor planet: any of numerous small celestial bodies that move around the sun


planetoid: any of numerous small celestial bodies that move around the sun


mire: a soft wet area of low-lying land that sinks underfoot


quagmire: a soft wet area of low-lying land that sinks underfoot


quag: a soft wet area of low-lying land that sinks underfoot


morass: a soft wet area of low-lying land that sinks underfoot


slack: a soft wet area of low-lying land that sinks underfoot


Mississippi: a major North American river and the chief river of the United States; rises in northern Minnesota and flows southward into the Gulf of Mexico


Mississippi River: a major North American river and the chief river of the United States; rises in northern Minnesota and flows southward into the Gulf of Mexico


Missouri: the longest river in the United States; arises in Montana and flows southeastward to become a tributary of the Mississippi at Saint Louis


Missouri River: the longest river in the United States; arises in Montana and flows southeastward to become a tributary of the Mississippi at Saint Louis


Mobile: a river in southwestern Alabama; flows into Mobile Bay


Mobile River: a river in southwestern Alabama; flows into Mobile Bay


Mobile Bay: a bay of the Gulf of Mexico; fed by the Mobile River


Mohawk River: a river of central New York that flows southeastward to the Hudson River


Mohorovicic discontinuity: the boundary between the Earth's crust and the underlying mantle


Moho: the boundary between the Earth's crust and the underlying mantle


molehill: a mound of earth made by moles while burrowing


monocline: a geological formation in which all strata are inclined in the same direction


Monongahela: a river that rises in northern West Virginia and flows north into Pennsylvania where it joins the Allegheny River at Pittsburgh to form the Ohio River


Monongahela River: a river that rises in northern West Virginia and flows north into Pennsylvania where it joins the Allegheny River at Pittsburgh to form the Ohio River


Mont Blanc: the highest mountain peak in the Alps; on the border between France and Italy to the south of Geneva (15,781 feet high)


Monte Bianco: the highest mountain peak in the Alps; on the border between France and Italy to the south of Geneva (15,781 feet high)


Monterey Bay: an inlet of the Pacific Ocean in western California


moon: any natural satellite of a planet


Moon: the natural satellite of the Earth


moon: the natural satellite of the Earth


moon: any object resembling a moon


moor: open land usually with peaty soil covered with heather and bracken and moss


moorland: open land usually with peaty soil covered with heather and bracken and moss


moraine: accumulated earth and stones deposited by a glacier


Moray Firth: an inlet of the North Sea on the northeast coast of Scotland


Moreau River: a river that rises in western South Dakota and flows eastward to the Missouri River


Moreton Bay: an arm of the Tasman Sea forming a bay to the east of Brisbane


morning star: a planet (usually Venus) seen just before sunrise in the eastern sky


daystar: a planet (usually Venus) seen just before sunrise in the eastern sky


Phosphorus: a planet (usually Venus) seen just before sunrise in the eastern sky


Lucifer: a planet (usually Venus) seen just before sunrise in the eastern sky


motor: a nonspecific agent that imparts motion


mountain: a land mass that projects well above its surroundings; higher than a hill


mount: a land mass that projects well above its surroundings; higher than a hill


mountain peak: the summit of a mountain


mountainside: the side or slope of a mountain


versant: the side or slope of a mountain


Mount Bartle Frere: the highest mountain peak in Queensland, Australia


Mount Carmel: a mountain range in northwestern Israel near the Mediterranean coast


Mount Elbert: the highest peak in the Rocky Mountains in central Colorado (14,431 feet high)


mouse nest: where mice bear and raise their young


mouse's nest: where mice bear and raise their young


mouth: the point where a stream issues into a larger body of water


mouth: an opening that resembles a mouth (as of a cave or a gorge)


Mozambique Channel: an arm of the Indian Ocean between Madagascar and southeastern Africa


mud puddle: a puddle of mud


mull: a term used in Scottish names of promontories


multiple star: a system of three or more stars associated by gravity


muon: an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino


negative muon: an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino


mu-meson: an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino and antineutrino


Murray: a southeast Australian river; flows westward and then south into the Indian Ocean at Adelaide


Murray River: a southeast Australian river; flows westward and then south into the Indian Ocean at Adelaide


Murrumbidgee: a river of southeastern Australia; flows westward into the Murray River


Murrumbidgee River: a river of southeastern Australia; flows westward into the Murray River


Musca: a small constellation in the polar region of the southern hemisphere near the Southern Cross and Chamaeleon


must: a necessary or essential thing


mutagen: any agent (physical or environmental) that can induce a genetic mutation or can increase the rate of mutation


Muztag: a highest mountain peak in the Kunlun Shan in China; near the Indian border (23,891 feet high)


Muztagh: a highest mountain peak in the Kunlun Shan in China; near the Indian border (23,891 feet high)


Nacimiento: a mountain peak in the Andes in Argentina (21,302 feet high)


nacreous cloud: a luminous iridescent cloud at a high altitude that may be seen when the sun is a few degrees below the horizon


mother-of-pearl cloud: a luminous iridescent cloud at a high altitude that may be seen when the sun is a few degrees below the horizon


Namoi: a river in southeastern Australia that flows generally northwest to join the Darling River


Namoi River: a river in southeastern Australia that flows generally northwest to join the Darling River


Nan: a river of western Thailand flowing southward to join the Ping River to form the Chao Phraya


Nan River: a river of western Thailand flowing southward to join the Ping River to form the Chao Phraya


Nanda Devi: a mountain in the Himalayas in northern India (25,660 feet high)


Nanga Parbat: a mountain in the Himalayas in Kashmir (26,660 feet high)


Nan Ling: a mountain range in southeastern China running generally east to west


Nares Deep: a depression in the floor of the Atlantic Ocean to the north of Haiti and Puerto Rico


Narragansett Bay: a deep inlet of the Atlantic Ocean in Rhode Island


narrow: a narrow strait connecting two bodies of water


natural depression: a sunken or depressed geological formation


depression: a sunken or depressed geological formation


natural elevation: a raised or elevated geological formation


elevation: a raised or elevated geological formation


natural order: the physical universe considered as an orderly system subject to natural (not human or supernatural) laws


nature: the natural physical world including plants and animals and landscapes etc.


nebula: an immense cloud of gas (mainly hydrogen) and dust in interstellar space


nebule: a small cloud


necessity: anything indispensable


essential: anything indispensable


requirement: anything indispensable


requisite: anything indispensable


necessary: anything indispensable


neck: a narrow elongated projecting strip of land


Neckar: a river in Germany; rises in the Black Forest and flows north into the Rhine


Neckar River: a river in Germany; rises in the Black Forest and flows north into the Rhine


need: anything that is necessary but lacking


want: anything that is necessary but lacking


neighbor: a nearby object of the same kind


neighbour: a nearby object of the same kind


Neosho: a river that rises in eastern Kansas and flows eastward into Oklahoma to become a tributary of the Arkansas River


Neosho River: a river that rises in eastern Kansas and flows eastward into Oklahoma to become a tributary of the Arkansas River


Neptune: a giant planet with a ring of ice particles; the 8th planet from the sun is the most remote of the gas giants


neritic zone: the ocean waters from the low tide mark to a depth of about 100 fathoms


nest: a structure in which animals lay eggs or give birth to their young


neutrino: an elementary particle with zero charge and zero mass


neutron: an elementary particle with 0 charge and mass about equal to a proton; enters into the structure of the atomic nucleus


neutron star: a star that has collapsed under its own gravity; it is composed of neutrons


Neva: a river in northwestern Russia flowing generally west into the Gulf of Finland


Neva River: a river in northwestern Russia flowing generally west into the Gulf of Finland


neve: the upper part of a glacier (beyond the limit of perpetual snow) where the snow turns to ice


New River: a river in the southeastern United States that flows northward from North Carolina to West Virginia where it empties into the Kanawha River


New York Bay: a bay of the North Atlantic; fed by the Hudson River


Niagara: a river flowing from Lake Erie into Lake Ontario; forms boundary between Ontario and New York


Niagara River: a river flowing from Lake Erie into Lake Ontario; forms boundary between Ontario and New York


Niagara: waterfall in Canada is the Horseshoe Falls; in the United States it is the American Falls


Niagara Falls: waterfall in Canada is the Horseshoe Falls; in the United States it is the American Falls


nidus: a nest in which spiders or insects deposit their eggs


Niger: an African river; flows into the South Atlantic


Niger River: an African river; flows into the South Atlantic


Nile: the world's longest river (4150 miles); flows northward through eastern Africa into the Mediterranean; the Nile River valley in Egypt was the site of the world's first great civilization


Nile River: the world's longest river (4150 miles); flows northward through eastern Africa into the Mediterranean; the Nile River valley in Egypt was the site of the world's first great civilization


nimbus: a dark grey cloud bearing rain


nimbus cloud: a dark grey cloud bearing rain


rain cloud: a dark grey cloud bearing rain


Niobrara: a tributary of the Missouri River


Niobrara River: a tributary of the Missouri River


nodule: (mineralogy) a small rounded lump of mineral substance (usually harder than the surrounding rock or sediment)


Norma: a small constellation in the southern hemisphere near Lupus and Ara in the Milky Way


normal fault: an inclined fault in which the hanging wall appears to have slipped downward relative to the footwall


gravity fault: an inclined fault in which the hanging wall appears to have slipped downward relative to the footwall


common fault: an inclined fault in which the hanging wall appears to have slipped downward relative to the footwall


North America: a continent (the third largest) in the western hemisphere connected to South America by the Isthmus of Panama


North Atlantic: that part of the Atlantic Ocean to the north of the equator


North Channel: a strait between Northern Ireland and Scotland that connects the Atlantic Ocean and the Irish Sea


Northern Cross: a cluster of 5 bright stars forming a cross in the constellation Cygnus


North Pacific: that part of the Pacific Ocean to the north of the equator


North Peak: 19,370 feet high


North Platte: a river that rises in northern Colorado and flows northward into Wyoming and then eastward and southeastward through Nebraska where it joins the South Platte to form the Platte River


North Platte River: a river that rises in northern Colorado and flows northward into Wyoming and then eastward and southeastward through Nebraska where it joins the South Platte to form the Platte River


North Sea: an arm of the North Atlantic between the British Isles and Scandinavia; oil was discovered under the North Sea in 1970


Norwegian Sea: the part of the Atlantic that lies off the Norwegian coast to the north of the North Sea


nova: a star that ejects some of its material in the form of a cloud and become more luminous in the process


nub: a small piece


stub: a small piece


nubbin: a small nub (especially an undeveloped fruit or ear of corn)


nucleon: a constituent (proton or neutron) of an atomic nucleus


nucleus: the positively charged dense center of an atom


nucleus: (astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail


nugget: a solid lump of a precious metal (especially gold) as found in the earth


nullah: a ravine or gully in southern Asia


Nuptse: a mountain in the central Himalayas on the border of Tibet and Nepal (25,726 feet high)


Ob: a major river of western Siberia; flows generally northward and westward to the Gulf of Ob and the Kara Sea


Ob River: a major river of western Siberia; flows generally northward and westward to the Gulf of Ob and the Kara Sea


obliterator: an eliminator that does away with all traces


ocean: a large body of water constituting a principal part of the hydrosphere


ocean floor: the bottom of a sea or ocean


sea floor: the bottom of a sea or ocean


ocean bottom: the bottom of a sea or ocean


seabed: the bottom of a sea or ocean


sea bottom: the bottom of a sea or ocean


Davy Jones's locker: the bottom of a sea or ocean


Davy Jones: the bottom of a sea or ocean


oceanfront: land bordering an ocean


Octans: the constellation that includes the southern celestial pole


Oder: a European river; flows into the Baltic Sea


Oder River: a European river; flows into the Baltic Sea


offing: the part of the sea that can be seen from the shore and is beyond the anchoring area


Ohio: a river that is formed in western Pennsylvania and flows westward to become a tributary of the Mississippi River


Ohio River: a river that is formed in western Pennsylvania and flows westward to become a tributary of the Mississippi River


oil-water interface: an interface forming the boundary between the non-miscible liquids oil and water


Ojos del Salado: a mountain in the Andes on the border between Argentina and Chile (22,572 feet high)


Okeechobee: a lake in southeast Florida to the north of the Everglades


Lake Okeechobee: a lake in southeast Florida to the north of the Everglades


Okefenokee Swamp: a large swampy area of northeast Florida and southeast Georgia


Old Faithful: a geyser in Yellowstone National Park that erupts for about 4 minutes about every 65 minutes


Olduvai Gorge: a gorge in northeastern Tanzania where anthropologists have found some of the earliest human remains


Olympus: a mountain peak in northeast Greece near the Aegean coast; believed by ancient Greeks to be the dwelling place of the gods (9,570 feet high)


Mount Olympus: a mountain peak in northeast Greece near the Aegean coast; believed by ancient Greeks to be the dwelling place of the gods (9,570 feet high)


Mt. Olympus: a mountain peak in northeast Greece near the Aegean coast; believed by ancient Greeks to be the dwelling place of the gods (9,570 feet high)


Olimbos: a mountain peak in northeast Greece near the Aegean coast; believed by ancient Greeks to be the dwelling place of the gods (9,570 feet high)


Omega Centauri: a global cluster in the constellation Centaurus


open chain: a chain of atoms in a molecule whose ends are not joined to form a ring


opening: an open or empty space in or between things


gap: an open or empty space in or between things


Ophiuchus: a large constellation in the equatorial region between Hercules and Scorpius


Orange: a river in South Africa that flows generally westward to the Atlantic Ocean


Orange River: a river in South Africa that flows generally westward to the Atlantic Ocean


ore bed: a stratum of ore


Orinoco: a South American river 1,500 miles long; flows into the South Atlantic


Orinoco River: a South American river 1,500 miles long; flows into the South Atlantic


Orion: a constellation on the equator to the east of Taurus; contains Betelgeuse and Rigel


Hunter: a constellation on the equator to the east of Taurus; contains Betelgeuse and Rigel


Osage: a river in Missouri that is a tributary of the Missouri River


Osage River: a river in Missouri that is a tributary of the Missouri River


Osaka Bay: a bay of the western Pacific in southern Honshu


Outaouais: a river in southeastern Canada that flows along the boundary between Quebec and Ontario to the Saint Lawrence River near Montreal


Ottawa: a river in southeastern Canada that flows along the boundary between Quebec and Ontario to the Saint Lawrence River near Montreal


Ottawa river: a river in southeastern Canada that flows along the boundary between Quebec and Ontario to the Saint Lawrence River near Montreal


Ouachita: a river that rises in western Arkansas and flows southeast into eastern Louisiana to become a tributary of the Red River


Ouachita River: a river that rises in western Arkansas and flows southeast into eastern Louisiana to become a tributary of the Red River


Ouse: a river in northeastern England that flows generally southeastward to join the Trent River and form the Humber


Ouse River: a river in northeastern England that flows generally southeastward to join the Trent River and form the Humber


outcrop: the part of a rock formation that appears above the surface of the surrounding land


outcropping: the part of a rock formation that appears above the surface of the surrounding land


rock outcrop: the part of a rock formation that appears above the surface of the surrounding land


outer planet: (astronomy) a major planet whose orbit is outside the asteroid belt (Jupiter, Saturn, Uranus, Neptune, Pluto)


outthrust: an outcropping of rock that extends outward


overburden: the surface soil that must be moved away to get at coal seams and mineral deposits


oxbow: a U-shaped curve in a stream


oxbow: the land inside an oxbow bend in a river


oxbow lake: a crescent-shaped lake (often temporary) that is formed when a meander of a river is cut off from the main channel


Ozarks: an area of low mountains in northwestern Arkansas and southeastern Missouri and northeastern Oklahoma


Ozark Mountains: an area of low mountains in northwestern Arkansas and southeastern Missouri and northeastern Oklahoma


Ozark Plateau: an area of low mountains in northwestern Arkansas and southeastern Missouri and northeastern Oklahoma


ozone hole: an area of the ozone layer (near the poles) that is seasonally depleted of ozone


ozone layer: a layer in the stratosphere (at approximately 20 miles) that contains a concentration of ozone sufficient to block most ultraviolet radiation from the sun


ozonosphere: a layer in the stratosphere (at approximately 20 miles) that contains a concentration of ozone sufficient to block most ultraviolet radiation from the sun


Pacific: the largest ocean in the world


Pacific Ocean: the largest ocean in the world


Pacific Coast: a coast of the Pacific Ocean


pack ice: a large expanse of floating ice


ice pack: a large expanse of floating ice


Pallas: a large asteroid; the second asteroid to be discovered


pallasite: a meteorite composed principally of olivine and metallic iron


Pamir Mountains: a mountain range in central Asia that is centered in Tajikistan but extends into Kyrgyzstan and Afghanistan and Pakistan and western China


the Pamirs: a mountain range in central Asia that is centered in Tajikistan but extends into Kyrgyzstan and Afghanistan and Pakistan and western China


Pangaea: (plate tectonics) a hypothetical continent including all the landmass of the earth prior to the Triassic period when it split into Laurasia and Gondwanaland


Pangea: (plate tectonics) a hypothetical continent including all the landmass of the earth prior to the Triassic period when it split into Laurasia and Gondwanaland


Para: an estuary in northern Brazil into which the Tocantins River flows


Para River: an estuary in northern Brazil into which the Tocantins River flows


Parana: a South American river; tributary of Rio de la Plata


Parana River: a South American river; tributary of Rio de la Plata


paring: a thin fragment or slice (especially of wood) that has been shaved from something


sliver: a thin fragment or slice (especially of wood) that has been shaved from something


shaving: a thin fragment or slice (especially of wood) that has been shaved from something


Parnaiba: a river in northeastern Brazil that flows generally northward to the Atlantic Ocean


Parnahiba: a river in northeastern Brazil that flows generally northward to the Atlantic Ocean


Parnassus: (Greek mythology) a mountain in central Greece where (according to Greek mythology) the Muses lived; known as the mythological home of music and poetry


Mount Parnassus: (Greek mythology) a mountain in central Greece where (according to Greek mythology) the Muses lived; known as the mythological home of music and poetry


Liakoura: (Greek mythology) a mountain in central Greece where (according to Greek mythology) the Muses lived; known as the mythological home of music and poetry


part: a portion of a natural object


piece: a portion of a natural object


particle: a body having finite mass and internal structure but negligible dimensions


subatomic particle: a body having finite mass and internal structure but negligible dimensions


pass: the location in a range of mountains of a geological formation that is lower than the surrounding peaks


mountain pass: the location in a range of mountains of a geological formation that is lower than the surrounding peaks


notch: the location in a range of mountains of a geological formation that is lower than the surrounding peaks


path: a line or route along which something travels or moves


track: a line or route along which something travels or moves


course: a line or route along which something travels or moves


Paulo Afonso: a major waterfall in northeastern Brazil


Paulo Afonso Falls: a major waterfall in northeastern Brazil


Pavo: a small constellation near the South Pole between Tucana and Ara


Pearl River: a river in Mississippi that flows southward to the Gulf of Mexico


pebble: a small smooth rounded rock


Pecos: a tributary of the Rio Grande that flows southeastward from New Mexico through western Texas


Pecos River: a tributary of the Rio Grande that flows southeastward from New Mexico through western Texas


Pee Dee: a river that flows through central North Carolina and northeastern South Carolina to the Atlantic Ocean


Pee Dee River: a river that flows through central North Carolina and northeastern South Carolina to the Atlantic Ocean


Pegasus: a constellation in the northern hemisphere near Andromeda and Pisces


peneplain: a more or less level land surface representing an advanced stage of erosion undisturbed by crustal movements


peneplane: a more or less level land surface representing an advanced stage of erosion undisturbed by crustal movements


peninsula: a large mass of land projecting into a body of water


Penobscot: a river in central Maine flowing into Penobscot Bay


Penobscot River: a river in central Maine flowing into Penobscot Bay


Penobscot Bay: an inlet of the Atlantic in eastern Maine


perforation: a hole made in something


Perejil: a small uninhabited Mediterranean islet claimed by both Morocco and Spain


permafrost: ground that is permanently frozen


Perseus: a conspicuous constellation in the northern hemisphere; between Auriga and Cassiopeia and crossed by the Milky Way


Persian Gulf: a shallow arm of the Arabian Sea between Iran and the Arabian peninsula; the Persian Gulf oil fields are among the most productive in the world


Arabian Gulf: a shallow arm of the Arabian Sea between Iran and the Arabian peninsula; the Persian Gulf oil fields are among the most productive in the world


petrifaction: a rock created by petrifaction; an organic object infiltrated with mineral matter and preserved in its original form


Phobos: the larger of the two satellites of Mars


Phoenix: a constellation in the southern hemisphere near Tucana and Sculptor


photoelectron: an electron that is emitted from an atom or molecule by an incident photon


photon: a quantum of electromagnetic radiation; an elementary particle that is its own antiparticle


photosphere: the intensely luminous surface of a star (especially the sun)


Pictor: a constellation in the southern hemisphere near Dorado and Columba


piedmont: a gentle slope leading from the base of a mountain to a region of flat land


Piedmont glacier: a type of glaciation characteristic of Alaska; large valley glaciers meet to form an almost stagnant sheet of ice


Piedmont type of glacier: a type of glaciation characteristic of Alaska; large valley glaciers meet to form an almost stagnant sheet of ice


Pike's Peak: a mountain peak in the Rockies in central Colorado (14,109 feet high)


Pillars of Hercules: the two promontories at the eastern end of the Strait of Gibraltar; according to legend they were formed by Hercules


pinetum: an area planted with pine trees or related conifers


Ping: a river in western Thailand; a major tributary of the Chao Phraya


Ping River: a river in western Thailand; a major tributary of the Chao Phraya


pion: a meson involved in holding the nucleus together; produced as the result of high-energy particle collision


pi-meson: a meson involved in holding the nucleus together; produced as the result of high-energy particle collision


Pisces: a large faint zodiacal constellation; between Aquarius and Aries


Pissis: a mountain in the Andes in Argentina (22,241 feet high)


pit: a sizeable hole (usually in the ground)


cavity: a sizeable hole (usually in the ground)


placer: an alluvial deposit that contains particles of some valuable mineral


plage: the beach at a seaside resort


plain: extensive tract of level open land


field: extensive tract of level open land


champaign: extensive tract of level open land


planet: (astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction


major planet: (astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction


planet: any celestial body (other than comets or satellites) that revolves around a star


planetary nebula: a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star


planetesimal: one of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system


plasmid: a small cellular inclusion consisting of a ring of DNA that is not in a chromosome but is capable of autonomous replication


plasmid DNA: a small cellular inclusion consisting of a ring of DNA that is not in a chromosome but is capable of autonomous replication


plate: a rigid layer of the Earth's crust that is believed to drift slowly


crustal plate: a rigid layer of the Earth's crust that is believed to drift slowly


Platte: a river in Nebraska that flows eastward to become a tributary of the Missouri River


Platte River: a river in Nebraska that flows eastward to become a tributary of the Missouri River


Pleiades: a star cluster in the constellation Taurus


Pluto: a small planet and the farthest known planet from the sun; it has the most elliptical orbit of all the planets


Po: a European river; flows into the Adriatic Sea


Po River: a European river; flows into the Adriatic Sea


Pobeda Peak: a mountain peak in the Tien Shan mountains in northern India (24,406 feet high)


Pobedy Peak: a mountain peak in the Tien Shan mountains in northern India (24,406 feet high)


point: a promontory extending out into a large body of water


polar glacier: a glacier near the Arctic or Antarctic poles


Polaris: the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it


North Star: the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it


pole star: the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it


polar star: the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it


polestar: the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it


polder: low-lying land that has been reclaimed and is protected by dikes (especially in the Netherlands)


Pollux: the brightest star in Gemini; close to Castor


polynya: a stretch of open water surrounded by ice (especially in Arctic seas)


pond: a small lake


pool: a small lake


pool: a small body of standing water (rainwater) or other liquid


puddle: a small body of standing water (rainwater) or other liquid


positron: an elementary particle with positive charge; interaction of a positron and an electron results in annihilation


antielectron: an elementary particle with positive charge; interaction of a positron and an electron results in annihilation


pothole: a pit or hole produced by wear or weathering (especially in a road surface)


chuckhole: a pit or hole produced by wear or weathering (especially in a road surface)


Potomac: a river in the east central United States; rises in West Virginia in the Appalachian Mountains and flows eastward, forming the boundary between Maryland and Virginia, to the Chesapeake Bay


Potomac River: a river in the east central United States; rises in West Virginia in the Appalachian Mountains and flows eastward, forming the boundary between Maryland and Virginia, to the Chesapeake Bay


Poyang: a lake in central China that is connected to the Chang Jiang by a canal


precipice: a very steep cliff


primary: (astronomy) a celestial body (especially a star) relative to other objects in orbit around it


prion: (microbiology) an infectious protein particle similar to a virus but lacking nucleic acid; thought to be the agent responsible for scrapie and other degenerative diseases of the nervous system


virino: (microbiology) a hypothetical infectious particle thought to be the cause of scrapie and other degenerative diseases of the central nervous system; consists of nucleic acid in a protective coat of host cell proteins


Procyon: the brightest star in Canis Minor


promontory: a natural elevation (especially a rocky one that juts out into the sea)


headland: a natural elevation (especially a rocky one that juts out into the sea)


head: a natural elevation (especially a rocky one that juts out into the sea)


foreland: a natural elevation (especially a rocky one that juts out into the sea)


protein molecule: any large molecule containing chains of amino acids linked by peptide bonds


proton: a stable particle with positive charge equal to the negative charge of an electron


Proxima: the nearest star to the sun; distance: 4.3 light years


Proxima Centauri: the nearest star to the sun; distance: 4.3 light years


Prudhoe Bay: a bay on the northern coast of Alaska where oil was discovered in 1968


pruning: something that has been pruned off of a plant


ptyalith: calculus in a salivary gland