morpheme

A morpheme is any of the smallest meaningful constituents within a linguistic expression and particularly within a word. Many words are themselves standalone morphemes, while other words contain multiple morphemes; in linguistic terminology, this is the distinction, respectively, between free and bound morphemes. The field of linguistic study dedicated to morphemes is called morphology.

In English, inside a word with multiple morphemes, the main morpheme that gives the word its basic meaning is called a root (such as cat inside the word cats), which can be bound or free. Meanwhile, additional bound morphemes, called affixes, may be added before or after the root, like the -s in cats, which indicates plurality but is always bound to a root noun and is not regarded as a word on its own. However, in some languages, including English and Latin, even many roots cannot stand alone; i.e., they are bound morphemes. For instance, the Latin root reg- ('king') must always be suffixed with a case marker: regis, regi, rex (reg+s), etc. The same is true of the English root nat(e) — ultimately inherited from a Latin root meaning "birth, born" — which appears in words like native, nation, nature, innate, and neonate.