Meaning of “overhear” - Learner’s Dictionary

overhear

verb [ T ] uk us /ˌəʊvəˈhɪər/ (past tense and past participle overheard)

to hear what someone is saying when they are not talking to you:

[ + doing sth ] I overheard him telling her he was leaving.

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