v. 1. To listen to a radio broadcast. We found them listening in to the president's speech. 2. To listen to the talk of others, often to talk that is not intended for your ears; eavesdrop. When Mary talked to her boyfriend on the telephone, her little brother listened in.
LISTEN IN
Meaning of LISTEN IN in English
American idioms English vocabulary. Английский словарь американских идиом. 2012