noun
past misdeed; past error; past folly; past sin
Rare, literary noun referring to a past wrongdoing, mistake, or foolish act. Often used in reflective or moral contexts.
彼は先非を悔いて、心を入れ替えた。
He repented of his past misdeeds and turned over a new leaf.
先非を改めることが大切だ。
It is important to correct one's past errors.