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in on (something)
Participating or involved in something, often something secret or exclusive. The conspiracy ran deep, and several members of the administration were in on it. Wow, that really was a surprise. Were you in on planning this?
*in on something
1. involved with something, such as an organization or an idea; informed about special plans. (*Typically: be ~; come ~; get ~; let someone ~.) There is a party upstairs, and I want to get in on it. I want to get in on your club's activities. Mary and Jane know a secret, but they won't let me in on it.
2. receiving a share of something. (*Typically: be ~; Come ~; get ~; let someone ~.) I want to get in on the new European business that is supposed to develop. We will all want to get in on the scheme.
Informed about; participating in: Only one business partner was not in on the illegal scheme.