Meaning of “defy” - Learner’s Dictionary

defy

verb uk us /dɪˈfaɪ/

[ T ] to refuse to obey someone or something:

Some of these children openly defy their teachers.
defy belief/description/explanation, etc

to be impossible to believe/describe/explain, etc:

His attitude defies belief.
defy sb to do sth

to tell someone to do something that you think will be impossible:

I defy you to prove that I'm wrong.

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