The difference between Citation form and Lemma

Citation form as a noun:

The basic form of a word used as a dictionary headword.

Lemma as a noun (mathematics):

A proposition proved or accepted for immediate use in the proof of some other proposition.

Lemma as a noun (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.

Lemma as a noun (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.

Lemma as a noun (botany):

The outer shell of a fruit or similar body.

Lemma as a noun (botany):

One of the specialized bracts around the floret in grasses.