In linguistics, a stem is a part of a word. The term is used with slightly different meanings.

In one usage, a stem is a form to which affixes can be attached. Thus, in this usage, the English word friendships contains the stem friend, to which the derivational suffix -ship is attached to form a new stem friendship, to which the inflectional suffix -s is attached. In a variant of this usage, the root of the word (in the example, friend) is not counted as a stem.

In a slightly different usage, which is adopted in the remainder of this article, a word has a single stem, namely the part of the word that is common to all its inflected variants. Thus, in this usage, all derivational affixes are part of the stem. For example, the stem of friendships is friendship, to which the inflectional suffix -s is attached.

Stems may be roots, e.g. run, or they may be morphologically complex, as in compound words (cf. the compound nouns meat ball or bottle opener) or words with derivational morphemes (cf. the derived verbs black-en or standard-ize). Thus, the stem of the complex English noun photographer is photo·graph·er, but not photo. For another example, the root of the English verb form destabilized is stabil-, a form of stable that does not occur alone; the stem is de·stabil·ize, which includes the derivational affixes de- and -ize, but not the inflectional past tense suffix -(e)d. That is, a stem is that part of a word that inflectional affixes attach to.

In language, a word is the smallest element 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 a rock 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 the English alphabet.

Stem may refer to:

STEM may refer to: