Illicit and Illegal

23/12/16 The difference between ‘Illicit’ & ‘Illegal’

Illicit

Unlawful or prohibited. For example, the laws may make it a crime to engage in “illicit trade” or possess “illicit drugs.”

Illegal

Against or not authorized by the law. Also called illicit or unlawful.

Basically, you will often have to determine whether to use illicit or illegal based on collocation and usage.