Meaning of “fool” - Learner’s Dictionary

fool

verb uk us /fuːl/

B2 [ T ] to trick someone:

Don't be fooled by his appearance.
[ + into + doing sth ] He fooled the old man into giving him the money.
you could have fooled me informal

something that you say when you do not believe what someone says about something that you saw or experienced yourself:

"I wasn't cross." "Really? You could have fooled me."

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