any language in which syntactic relations within sentences are expressed by inflection (the change in the form of a word that indicates distinctions of tense, person, gender, number, mood, voice, and case) or by agglutination (word formation by means of morpheme, or word unit, clustering). Latin is an example of an inflected language; Hungarian and Finnish are examples of agglutinative languages.

Highly synthetic languages, in which a whole sentence may consist of a single word (usually a verb form) containing a large number of affixes are called polysynthetic. Eskimo and many American Indian languages are polysynthetic. See also agglutination; inflection. Compare analytic language.