from
The Collaborative International Dictionary of English v.0.48
Lemma \Lem"ma\ (l[e^]m"m[.a]), n.; pl. L. {Lemmata}
(-m[.a]*t[.a]), E. {Lemmas} (-m[.a]z). [L. lemma, Gr. lh^mma
anything received, an assumption or premise taken for
granted, fr. lamba`nein to take, assume. Cf. {Syllable}.]
1. (Math., Logic) A preliminary or auxiliary proposition
demonstrated or accepted for immediate use in the
demonstration of some other proposition, as in mathematics
or logic.
[1913 Webster]
2. A word that is included in a glossary or list of
headwords; a headword.
[PJC]