Meaning of “illegal” - Learner’s Dictionary

illegal

adjective us uk /ɪˈliːɡəl/

B2 not allowed by law:

illegal drugs/weapons
[ + to do sth ] It is illegal to sell cigarettes to anyone under 16.

More examples

illegally adverb

B2

an illegally parked car

(Definition of “illegal” from the Cambridge Learner’s Dictionary © Cambridge University Press)