JLPT Level: N2
Meanings

Classical negative marker

Classical verb negation (not)

Literary negation auxiliary used with the irrealis form of verbs

Usage

動詞の未然形 + ぬ

Explanation
ぬ is a classical (literary) negative auxiliary that attaches to the 未然形 (irrealis form) of a verb to indicate negation. It is primarily found in classical Japanese texts, poetry, or stylized modern writings. It carries a stronger, more formal or archaic nuance than ない, and can also convey a sense of negation in general statements or narration in old literature. In modern usage, it can appear in historical dramas or quotes to evoke antiquity. ぬ is not used in everyday conversation in contemporary Japanese.
彼はそれを語はぬ。
かれはそれをかたらぬ。

He will not say that.

この謎は誰も解くぬ。
このなぞはだれもとくぬ。

No one can solve this mystery (in the classical sense).