verb (intr, adverb often foll by to)
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Idioms and Phrases with listen in
Hear or overhear the conversation of others; eavesdrop. It is also put as listen in on, as in She listened in on her parents and learned they were planning a surprise party. [Early 1900s]
Tune in and listen to a broadcast, as in Were you listening in the other night when they played Beethoven's Fifth? [1920s]