Illicit a. : Not permitted or allowed; prohibited; unlawful; as, illicit trade; illicit intercourse; illicit pleasure.

Example:
How do I get someone (50years old) to stop using Illicit drugs?

Taxonomy
illicit, Merriam-Webster Online Dictionary, Dictionary, webster, Word Games, Webster Online Dictionary with audio pronunciations, thesaurus, Google Search, Custom Search, glossary, english, language, ESL, Search, adjective, Etymology, Latin, ly.

Defination from the web:
illicit from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... Learn more about "illicit" and related topics at Britannica.com. Pronunciation Symbols. Share this entry: Link to this page: Cite this page: Products ...