From Middle English nai, nei, from Old Norse nei (“no”), contraction of ne (“not”) + ei (“ever”), itself from Proto-Germanic *nai (“never”), *nē (“not”). More at no.
- (archaic) No.
- or even, or more like, or should I say. Introduces a stronger and more appropriate expression than the preceding one.
nay (plural nays)
- A vote against.
- A person who voted against.
- (archaic) A denial; a refusal. 
nay (third-person singular simple present nays, present participle naying, simple past and past participle nayed)
- (obsolete) To refuse.
nay (not comparable)
- (obsolete) Nary. (Can we add an example for this sense?)