Definition - (Aka canonical form | dictionary form | citation form)

A lexeme is a set of words that have the same base form and a lemma is the member of the set that is chosen by convention to represent it as, for example, the headword in a dictionary.

For example, run, runs, ran and running are all forms of the same lexeme; run is the lemma.

Etymology -
The word means "a premiss" in Greek.

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