Definition of "lemma"

(mathematics) A proposition proved or accepted for immediate use in the proof of some other proposition.  examples

(linguistics, lexicography) The canonical form of an inflected word; i.e., the form usually found as the headword in a dictionary, such as the nominative singular of a noun, the bare infinitive of a verb, etc.  examples

(psycholinguistics) The theoretical abstract conceptual form of a word, representing a specific meaning, before the creation of a specific phonological form as the sounds of a lexeme, which may find representation in a specific written form as a dictionary or lexicographic word.  examples

(botany) The outer shell of a fruit or similar body.  examples

(botany) One of the specialized bracts around the floret in grasses.  examples