It is an adverb, an interjection, and an adjective.
An adverb - Did you talk to your brother last night? No, i didn't. "I didn't" is a sentence, but "NO" makes it more emphatic, so "NO"acts as an adverb here.
Interjection- NO
An adjective - He is "NO" novice when it comes to politics. Here "NO" acts as an adjective because it modifies NOVICE, which is a noun.
part of speech
The part of speech for this particular word is a noun.
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The part of speech for "explicit" is an adjective.
The part of speech for "twirl" is a verb.
The part of speech for "unfamiliar" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "lecturer" is a noun.
The part of speech for "indefinite" is an adjective.
The part of speech for "buried" is a verb.