Meaning of “criminal” - Learner’s Dictionary

criminal

adjective uk us /ˈkrɪmɪnəl/
ABOUT CRIME [ always before noun ]

B2 relating to crime:

criminal activity
He has a criminal record (= the police have an official record of his crimes).
BAD informal

very bad or morally wrong:

It's criminal that people are having to wait so long for hospital treatment.
criminally adverb

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