Word

In language, a word is the smallest free form that may be uttered in isolation with semantic or pragmatic content (with literal or practical meaning). This contrasts with a morpheme, which is the smallest unit of meaning but will not necessarily stand on its own. A word may consist of a single morpheme (for example: oh!, rock, red, quick, run, expect), or several (rocks, redness, quickly, running, unexpected), whereas a morpheme may not be able to stand on its own as a word (in the words just mentioned, these are -s, -ness, -ly, -ing, un-, -ed).

A complex word will typically include a root and one or more affixes (rock-s, red-ness, quick-ly, run-ning, un-expect-ed), or more than one root in a compound (black-board, rat-race). Words can be put together to build larger elements of language, such as phrases (a red rock), clauses (I threw a rock), and sentences (he threw one too but he missed).

The term word may refer to a spoken word or to a written word, or sometimes to the abstract concept behind either. Spoken words are made up of units of sound called phonemes, and written words of symbols called graphemes, such as the letters of English.

Definitions
The ease or difficulty of deciphering a word depends on the language. 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.

Semantic definition
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).

Some semanticists have proposed 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 "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.

Word boundaries
The task of defining what constitutes a "word" involves determining where one word ends and another word begins&mdash;in other words, identifying word boundaries. There are several ways to determine where the word boundaries of spoken language should be placed:
 * Potential pause: A speaker is told to repeat a given sentence slowly, allowing for pauses. The speaker will tend to insert pauses at the word boundaries. However, this method is not foolproof: the speaker could easily break up polysyllabic words, or fail to separate two or more closely related words.
 * Indivisibility: A speaker is told to say a sentence out loud, and then is told to say the sentence again with extra words added to it. Thus, I have lived in this village for ten years might become My family and I have lived in this little village for about ten or so years. These extra words will tend to be added in the word boundaries of the original sentence. However, some languages have infixes, which are put inside a word. Similarly, some have separable affixes; in the German sentence "Ich komme gut zu Hause an", the verb ankommen is separated.
 * Phonetic boundaries: Some languages have particular rules of pronunciation that make it easy to spot where a word boundary should be. For example, in a language that regularly stresses the last syllable of a word, a word boundary is likely to fall after each stressed syllable. Another example can be seen in a language that has vowel harmony (like Turkish): the vowels within a given word share the same quality, so a word boundary is likely to occur whenever the vowel quality changes. Nevertheless, not all languages have such convenient phonetic rules, and even those that do present the occasional exceptions.
 * Orthographic boundaries: See below.

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. Examples are ice cream, air raid shelter, get up, and these must thus be considered as more than one word. (Ice, cream, air etc. indisputably exist as free forms, the case of get is less clear.) In contrast, brownstone is spelt as a single word and would thus be considered as such for most purposes even though brown and stone are free forms.

Vietnamese orthography, although using the Latin alphabet, delimits monosyllabic morphemes, not words. East Asian orthography (languages using CJK characters) also tend to delimit syllables (in the case of Chinese characters) or morae (in the case of kana) rather than full words. Hangul the Korean alphabet, delimits both syllables and words, by grouping graphemes into syllabic blocks but also adds spaces between 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.

Morphology
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
 * the root
 * optional suffixes
 * a desinence.
 * 1) ', the zero grade of the root '
 * 2) a root-extension ' (diachronically a suffix), resulting in a complex root '
 * 3) The thematic suffix 
 * 4) the neuter gender nominative or accusative singular desinence .

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 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 desinences taken by the word.