1. 非法的;违禁的;不正当的
An illicit activity or substance is not allowed by law or the social customs of a country.

1. contrary to or forbidden by law

e.g. an illegitimate seizure of power
illicit trade
an outlaw strike
unlawful measures

Synonym: illegitimateoutlaw(a)outlawedunlawful

2. contrary to accepted morality (especially sexual morality) or convention

e.g. an illicit association with his secretary