A somewhat formal or literary term for morally wrong acts or wickedness. Often used in contrast with 善 (ぜん, good).
彼は善と不善の区別がつかない。
He cannot tell the difference between good and evil.
不善を働いた者は罰せられるべきだ。
Those who commit evil deeds should be punished.
negative reaction; unsuccessful vaccination
Compound of 不 (ふ, 'not') and 善 (ぜん, 'good'), literally 'not good'. The word follows a common Sino-Japanese pattern for forming abstract nouns denoting the absence of a positive quality.