unlawful forbidden 
[Adjective] Against the law or not accepted by a society.
[adj] - contrary to accepted morality (especially sexual morality) or convention
Il·lic'it adjective [ Latin illicitus ; prefix il- not + licitus , past participle of licere to be allowed or permitted: confer French illicite . See In- not, and License .] Not permitted or allowed; prohibited; unlawful; as, illicit trade; 
adjective contrary to accepted morality (especially sexual morality) or convention; `an illicit association with his secretary`
• (a.) Not permitted or allowed; prohibited; unlawful; as, illicit trade; illicit intercourse; illicit pleasure.
illicit 1. Not allowed by the law. 2. Considered wrong or unacceptable by prevailing social customs or standards. 3. Disapproved of or not permitted for moral or ethical reasons.
Refer to the definition for illegal.
contrary to accepted morality or convention