Morpheme

Etymology

From French morphème, coined on the model of phonème, from Greek morphē ("form, shape"). Where phoneme captures a unit of sound, morpheme captures a unit of form-with-meaning. Some morphemes stand alone as words ("book"); others, like the prefix "re-" or the plural "-s," carry meaning only when attached.

noun · /MOR-feem/
The smallest unit of language that carries meaning, whether a whole word or a piece of one.
What it names
The meaning-bearing building blocks below the word — why "un-friend-ly" is one word but three meaningful parts.
Example
The word "unhappiness" packs three morphemes: "un-," "happy," and "-ness."
Related idea
A morpheme is the smallest meaningful unit; a phoneme is the smallest distinctive sound, carrying no meaning of its own. Morphemes are what meaning is built from; phonemes are what they’re spoken with.