- illicit - contrary to accepted morality (especially sexual morality) or convention; "an illicit association with his secretary"
Antonym: licit
- illegitimate, illicit, outlaw, outlawed, unlawful - contrary to or forbidden by law; "an illegitimate seizure of power"; "illicit trade"; "an outlaw strike"; "unlawful measures"
Antonym: legal (indirect, via illegal)