Definition of "No" :

noun: a negative

"His no was loud and clear."

noun: a radioactive transuranic element synthesized by bombarding curium with carbon ions; 7 isotopes are known

adjective: (quantifier) used with either mass nouns or plural count nouns for indicating a complete or almost complete lack or zero quantity of

"We have no bananas."

adverb: used to express refusal or denial or disagreement etc or especially to emphasize a negative statement

"No, you are wrong."

adverb: not in any degree or manner; not at all

"He is no better today."

adverb: referring to the degree to which a certain quality is present

"He was no heavier than a child."