* Formal: The detective uncovered evidence of illicit financial dealings between the two companies.
* Neutral: The museum's collection includes artifacts from the illicit trade of ancient relics.
* Informal: They got caught trying to sneak illicit snacks into the movie theater.
* Figurative: The artist's illicit blend of colors created a mesmerizing and unexpected effect.
The best way to use "illicit" depends on the context and tone you want to create.