Meaning

noun a negative

adverb not this merely but also; not only so but

originFrom 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. The verb is from Middle English nayen (“to refuse, deny, gainsay”), from the interjection and adverb above.

Etymology from Wiktionary, CC BY-SA 3.0