What it means
ぬ is a classical and literary negative auxiliary meaning “not” or “does not.” It attaches to a verb’s negative stem, such as 書かぬ from 書く, and is commonly found in literary writing, historical styles, proverbs, and fixed expressions. Although it is placed in the non-polite register slot here, it is not an ordinary modern familiar ending and should not be used as a casual equivalent of ない.
Usage note
ぬ is not a polite counterpart of ない or ません. Its literary or archaic tone can sound unnatural in ordinary modern conversation, so learners should usually use ない in plain speech and ません in polite speech instead.
Example sentences
祖父は、約束を破る者を決して許さぬ人だった。
My grandfather was a person who never forgave those who broke promises.
古い記録には、村人は冬の間、この峠を越えぬと記されている。
The old records state that the villagers do not cross this mountain pass during the winter.