An Etymological Dictionary of Astronomy and Astrophysics

1. A subsidiary proposition, proved for use in the proof of another proposition.
   

2. Linguistics: A word considered as its citation form together with all the → inflected forms. For example, the lemma go
   consists of go together with goes, going, went, and gone.
   

3. An argument or theme, especially when used as the subject or title of a composition (Dictionary.com).

Etymology (EN): From L. lemma, from Gk. lemma “something received or taken; an argument; something taken for granted,” from root of lambanein “to take,” → analemma.

Etymology (PE): Nehak, from neh present stem of nehâdan “to place, put; to set,” → position, + -ak a diminutive suffix of nouns.