sit in
sit in {v.}
1. To be a member; participate.
We're having a conference and we'd like you to sit in.
also sit in on: To be a member of; participate in.
We want you to sit in on the meeting.
2. To attend but not participate. Often used with "on".
Our teacher was invited to sit in on the conference.
Compare: LOOK ON.
Categories:
Source: A Dictionary of American Idioms
