A morpheme is the smallest unit of language that carries meaning. It may be a whole word or a part of a word such as a prefix, suffix, or inflection.

The word “unhappiness” contains three morphemes: “un-,” “happy,” and “-ness.” Each contributes meaning. Free morphemes can stand alone as words; bound morphemes must attach to other forms. Languages differ in how they pack meaning into morphemes. Some rely heavily on inflection; others use relatively fixed word forms and convey relationships through word order and separate particles.

Children acquire the morphological system of their language gradually, sometimes overgeneralizing rules (“goed” instead of “went”) before mastering exceptions. Disorders of language can selectively impair morphological processing. Linguists analyze morphemes to describe the internal structure of words and the rules that generate new forms.

Meaning in language begins with the morpheme, the smallest piece that still means something.