Word

In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with objective or practical meaning. In many languages, words also correspond to sequences of graphemes ("letters") in their standard writing systems that are delimited by spaces wider than the normal inter-letter space, or by other graphical conventions. The concept of "word" is usually distinguished from that of a morpheme, which is the smallest unit of word which has a meaning, even if it will not stand on its own.
In many languages, the notion of what constitutes a "word" may be mostly learned as part of learning the writing system. This is the case for the English language, and for most languages that are written with alphabets derived from the ancient Latin or Greek alphabets.
There still remains no consensus among linguists about the proper definition of "word" in a spoken language that is independent of its writing system, nor about the precise distinction between it and "morpheme". This issue is particularly debated for Chinese and other languages of East Asia, and may be moot for Afro-Asiatic languages.
In English orthography, the letter sequences "rock", "god", "write", "with", "the", "not" are considered to be single-morpheme words, whereas "rocks", "ungodliness", "typewriter", and "cannot" are words composed of two or more morphemes ("rock"+"s", "un"+"god"+"li"+"ness", "type"+"writ"+"er", and "can"+"not"). In English and many other languages, the morphemes that make up a word generally include at least one root (such as "rock", "god", "type", "writ", "can", "not") and possibly some affixes ("-s", "un-", "-ly", "-ness"). Words with more than one root ("[type][writ]er", "[cow][boy]s", "[tele][graph]ically") are called compound words.
Words are combined to form other elements of language, such as phrases ("a red rock", "put up with"), clauses ("I threw a rock"), and sentences ("I threw a rock, but missed").
Definitions/meanings.
Summary.
There have been many proposed criteria for identifying words. However, no definition has been found to apply to all languages. Dictionaries categorize a language's lexicon (i.e., its vocabulary) into lemmas. These can be taken as an indication of what constitutes a "word" in the opinion of the writers of that language. The most appropriate means of measuring the length of a word is by counting its syllables or morphemes. When a word has multiple definitions or multiple senses, it may result in confusion in a debate or discussion.
Semantic definition.
Leonard Bloomfield introduced the concept of "Minimal Free Forms" in 1928. Words are thought of as the smallest meaningful unit of speech that can stand by themselves. This correlates phonemes (units of sound) to lexemes (units of meaning). However, some written words are not minimal free forms as they make no sense by themselves (for example, "the" and "of").
Some semanticists have put forward a theory of so-called semantic primitives or semantic primes, indefinable words representing fundamental concepts that are intuitively meaningful. According to this theory, semantic primes serve as the basis for describing the meaning, without circularity, of other words and their associated conceptual denotations.
Features.
In the Minimalist school of theoretical syntax, words (also called "lexical items" in the literature) are construed as "bundles" of linguistic features that are united into a structure with form and meaning. For example, the word "koalas" has semantic features (it denotes real-world objects, koalas), category features (it is a noun), number features (it is plural and must agree with verbs, pronouns, and demonstratives in its domain), phonological features (it is pronounced a certain way), etc.
Word boundaries.
The task of defining what constitutes a "word" involves determining where one word ends and another word begins—in other words, identifying word boundaries. There are several ways to determine where the word boundaries of spoken language should be placed:
Orthography.
In languages with a literary tradition, there is interrelation between orthography and the question of what is considered a single word. Word separators (typically spaces) are common in modern orthography of languages using alphabetic scripts, but these are (excepting isolated precedents) a relatively modern development (see also history of writing).
In English orthography, compound expressions may contain spaces. For example, "ice cream", "air raid shelter" and "get up" each are generally considered to consist of more than one word (as each of the components are free forms, with the possible exception of "get"), and so is "no one", but the similarly compounded "someone" and "nobody" are considered single words.
Not all languages delimit words expressly. Mandarin Chinese is a very analytic language (with few inflectional affixes), making it unnecessary to delimit words orthographically. However, there are many multiple-morpheme compounds in Mandarin, as well as a variety of bound morphemes that make it difficult to clearly determine what constitutes a word.
Sometimes, languages which are extremely close grammatically will consider the same order of words in different ways. For example, reflexive verbs in the French infinitive are separate from their respective particle, e.g. "se laver" ("to wash oneself"), whereas in Portuguese they are hyphenated, e.g. "lavar-se", and in Spanish they are joined, e.g. "lavarse".
Japanese uses orthographic cues to delimit words, such as switching between kanji (Chinese characters) and the two kana syllabaries. This is a fairly soft rule, because content words can also be written in hiragana for effect (though if done extensively spaces are typically added to maintain legibility).
Vietnamese orthography, although using the Latin alphabet, delimits monosyllabic morphemes rather than words.
In character encoding, word segmentation depends on which characters are defined as word dividers.
Morphology.
Morphology is the study of word formation and structure. In synthetic languages, a single word stem (for example, "love") may have a number of different forms (for example, "loves", "loving", and "loved"). However, for some purposes these are not usually considered to be different words, but rather different forms of the same word. In these languages, words may be considered to be constructed from a number of morphemes.
In Indo-European languages in particular, the morphemes distinguished are:
Thus, the Proto-Indo-European " would be analyzed as consisting of
Philosophy.
Philosophers have found words objects of fascination since at least the 5th century BC, with the foundation of the philosophy of language. Plato analyzed words in terms of their origins and the sounds making them up, concluding that there was some connection between sound and meaning, though words change a great deal over time. John Locke wrote that the use of words "is to be sensible marks of ideas", though they are chosen "not by any natural connexion that there is between particular articulate sounds and certain ideas, for then there would be but one language amongst all men; but by a voluntary imposition, whereby such a word is made arbitrarily the mark of such an idea". Wittgenstein's thought transitioned from a word as representation of meaning to "the meaning of a word is its use in the language."
Classes.
Grammar classifies a language's lexicon into several groups of words. The basic bipartite division that is possible for virtually every natural language is that of nouns vs. verbs.
The classification into such classes is in the tradition of Dionysius Thrax, who distinguished eight categories: noun, verb, adjective, pronoun, preposition, adverb, conjunction and interjection.
In Indian grammatical tradition, Pāṇini introduced a similar fundamental classification into a nominal (nāma, suP) and a verbal (ākhyāta, tiN) class, based on the set of suffixes taken by the word. Some words can be controversial, such as slang in formal contexts; misnomers, due to them not meaning what they would imply; or polysemous words, due to the potential confusion between their various senses.