A word is the smallest free form (an item that may be uttered in isolation with semantic or pragmatic content) in a language, in contrast to a morpheme, which is the smallest unit of meaning. A word may consist of only one morpheme (e.g. wolf), but a single morpheme may not be able to exist as a free form (e.g. the English plural morpheme -s).
Typically, a word will consist of a root or stem, and zero or more affixes. Words can be combined to create other units of language, such as phrases, clauses, and/or sentences. A word consisting of two or more stems joined together form a compound. A word combined with an already existing word or part of a word form a portmanteau.
Depending upon language in question, it can be either easy or difficult to identify or decipher a word. Dictionaries take upon themselves the task of categorizing 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.
Leonard Bloomfield introduced the concept of "Minimal Free Forms" in 1926. 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).
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 "bears" has semantic features (it denotes real-world objects, bears), 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.
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:
In practice, linguists apply a mixture of all these methods to determine the word boundaries of any given sentence. Even with the careful application of these methods, the exact definition of a word is often still very elusive.
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 modern development (see also history of writing).
Vietnamese orthography, although using the Latin alphabet, delimits monosyllabic morphemes, not words. East Asian orthography (languages using CJK characters) also tend to delimit syllables rather than full words. Conversely, synthetic languages often combine many lexical morphemes into single words, making it difficult to boil them down to the traditional sense of words found more easily in analytic languages; this is especially difficult for polysynthetic languages, such as Inuktitut and Ubykh, where entire sentences may consist of a single word.
In synthetic languages, a single word stem (for example, love) may have a number of different forms (for example, loves, loving, and loved). However, these are not usually considered to be different words, but 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 *wr̥dhom would be analyzed as consisting of
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."
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 desinences taken by the word.