Illicit means forbidden by law, rules, or custom. When something is illicit, it's not allowed, whether that's because it breaks an actual law or violates important rules that everyone's supposed to follow.

An illicit trade might involve selling things that are illegal to sell, like smuggling goods across a border without permission. Students caught in illicit communication during a test are breaking their school's rules about working independently. A spy might make an illicit copy of secret documents, doing something clearly forbidden.

The word carries a sense of secrecy and wrongdoing. Illicit activities happen in the shadows because people know they shouldn't be doing them. This makes illicit different from something that's merely discouraged or frowned upon. If your teacher asks you not to chew gum in class, that's not quite illicit. But if students sneak into the school at night when it's locked and off-limits, that's an illicit entry.

You might confuse illicit with elicit, which sounds almost identical but means something completely different: to draw out or bring out a response. The teacher tried to elicit answers from her students, but discovered their illicit use of phones during the quiz.