I am not sure if there is a real difference. However, it's not very common to say 'licit' in normal speech. In fact, I had to think for a moment about that word before I responded. Illicit, however, is used commonly when talking about drugs. It's a word you'll hear often on the news in the place of 'illegal'. "Two men were arrested today for possession of illicit drugs." "One person was arrested today after getting caught performing illicit activities." So in summary, in normal speech we would just say legal / illegal. But it's a bit more formal to say illicit, and rare to hear licit. Hope this helps!