a (mathematics) Having the properties of an inverse.
a (Kiowa-Tanaon linguistics) A grammatical number marking that indicates the opposite grammatical number (or numbers) of the default number specification of noun class.
n The opposite of a given, due to contrary nature or effect.
n (mathematics) The inverse of an element x with respect to a binary operation is an element that when combined with x yields the appropriate identity element.
n (context|logic) A statement constructed from the negatives of the premise and conclusion of some other statement: ~p → ~q is the inverse of p → q.