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listen in(on someone or something)
1. to join someone or a group as a listener. The band is rehearsing. Let's go listen in on them. It won't hurt to listen in, will it?
2. to eavesdrop on someone. Please don't try to listen in on us. This is a private conversation. I am not listening in. I was here first. You are talking too loud.
1. 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]
2. Tune in and listen to a broadcast, as in Were you listening in the other night when they played Beethoven's Fifth? [1920s]
1. To listen to something or to someone conversing without participating in the conversation: It is rude to listen in on other people's conversations. We put our ears to the door and listened in.
2. To tune in and listen to a broadcast: Listen in next week to the conclusion of our jazz concert series!