Opposite (semantics)

In lexical semantics, opposites are words lying in an inherently incompatible binary relationship. For example, something that is "long" entails that it is not "short". It is referred to as a 'binary' relationship because there are two members in a set of opposites. The relationship between opposites is known as opposition. A member of a pair of opposites can generally be determined by the question "What is the opposite of  X ?"
The term antonym (and the related antonymy) is commonly taken to be synonymous with opposite, but antonym also has other more restricted meanings. Graded (or gradable) antonyms are word pairs whose meanings are opposite and which lie on a continuous spectrum (hot, cold). Complementary antonyms are word pairs whose meanings are opposite but whose meanings do not lie on a continuous spectrum ("push", "pull"). Relational antonyms are word pairs where opposite makes sense only in the context of the relationship between the two meanings ("teacher", "pupil"). These more restricted meanings may not apply in all scholarly contexts, with Lyons (1968, 1977) defining antonym to mean gradable antonyms, and Crystal (2003) warning that antonymy and antonym should be regarded with care.
General discussion.
Opposition is a semantic relation in which one word has a sense or meaning that negates or is, in the sense of scale, distant from a related word. Other words are capable of being opposed, but the language in question has an accidental gap in its lexicon. For example, the word "devout" lacks a lexical opposite, but it is fairly easy to conceptualize a parameter of devoutness where "devout" lies at the positive pole with a missing member at the negative pole. Opposites of such words can nevertheless sometimes be formed with the prefixes "un-" or "non-", with varying degrees of naturalness. For example, the word "undevout" appears in Webster's dictionary of 1828, while the pattern of "non-person" could conceivably be extended to "non-platypus". Conversely, some words appear to be a prefixed form of an opposite, but the opposite term does not exist, such as "inept," which appears to be "in-" + *"ept;" such a word is known as an unpaired word.
Opposites may be viewed as a special type of incompatibility. Words that are incompatible create the following type of entailment (where "X" is a given word and "Y" is a different word incompatible with word X):
An example of an incompatible pair of words is "cat : dog":
This incompatibility is also found in the opposite pairs "fast : slow" and "stationary : moving", as can be seen below:
"It's fast"  entails  "It's not slow" 
Cruse (2004) identifies some basic characteristics of opposites:
Some planned languages abundantly use such devices to reduce vocabulary multiplication. Esperanto has "mal-" (compare "bona" = "good" and "malbona" = "bad"), Damin has "kuri-" ("tjitjuu" "small", "kuritjitjuu" "large") and Newspeak has "un-" (as in "ungood", "bad").
Some classes of opposites include:
Types of antonyms.
An antonym is one of a pair of words with opposite meanings. Each word in the pair is the antithesis of the other. A word may have more than one antonym. There are three categories of antonyms identified by the nature of the relationship between the opposed meanings. Where the two words have definitions that lie on a continuous spectrum of meaning, they are gradable antonyms. Where the meanings do not lie on a continuous spectrum and the words have no other lexical relationship, they are complementary antonyms. Where the two meanings are opposite only within the context of their relationship, they are relational antonyms.
Gradable antonyms.
A gradable antonym is one of a pair of words with opposite meanings where the two meanings lie on a continuous spectrum. Temperature is such a continuous spectrum so "hot" and "cold", two meanings on opposite ends of the spectrum, are gradable antonyms. Other examples include: "heavy" : "light", "fat" : "skinny", "dark" : "light", "young" : "old", "early" : "late", "empty" : "full", "dull" : "interesting".
Complementary antonyms.
A complementary antonym, sometimes called a binary or contradictory antonym (Aarts, Chalker & Weiner 2014), is one of a pair of words with opposite meanings, where the two meanings do not lie on a continuous spectrum. There is no continuous spectrum between "odd" and "even" but they are opposite in meaning and are therefore complementary antonyms. Other examples include: "mortal" : "immortal", "exit" : "entrance", "exhale" : "inhale", "occupied" : "vacant".
Relational antonyms.
A relational antonym is one of a pair of words that refer to a relationship from opposite points of view. There is no lexical opposite of "teacher", but "teacher" and "pupil" are opposite within the context of their relationship. This makes them relational antonyms. Other examples include: "husband" : "wife", "doctor" : "patient", "predator" : "prey", "teach" : "learn", "servant" : "master", "come" : "go", "parent" : "child".
Auto-antonyms.
An auto-antonym is a word that can have opposite meanings in different contexts or under separate definitions: