A morpheme is the smallest piece of a language that still means something. It is not a letter, and it is not a beat of sound. It is a bit of meaning you can point to. Some words are only one morpheme: so, the, boy, banana. You cannot cut them into smaller meaning-pieces and still have English. Other words are built from more than one. Boys is boy plus the plural -s. Unhappiness is un- plus happy plus -ness. Each of those pieces does a job: un- turns the meaning over, -ness makes an idea-noun, -s marks “more than one.” A morpheme can be a whole word, or a little add-on that never stands alone, like -ed or re-. Teachers use this word in language class, not in ordinary chat. People who are not linguists almost never say it. Though actually, students often mix it up with “syllable,” because both feel like “small bits of a word.” They are different cuts. Dogs is one syllable when you say it, and two morphemes on the page of meaning.

語素（語言裡最小的意義單位；也有人說詞素）