Illicit

google

ref

early 16th century: from French, or from Latin illicitus, from in- ‘not’ + licitus (see licit).

wiktionary

ref

Borrowed from French illicite, from Latin illicitus, from in-(“not”) + licitus(“allowed, permitted”), from licet(“it is allowed”).

etymonline

ref

illicit (adj.)

c. 1500, from Old French illicite "unlawful, forbidden" (14c.), from Latin illicitus "not allowed, unlawful, illegal," from assimilated form of in- "not, opposite of" (see in- (1)) + licitus "lawful," past participle of licere "to be allowed" (see licence (n.)). Related: Illicitly.