Definition
Being or made privy to, a participant in, involved in, included in, or informed of (usually something private or secret, especially a plan or plot).
Origins
Extracted from let in on.
In Context
- "She was in on the surprise from the beginning."
- "He didn't hold the gun, but he got in on the robbery after he overheard some of us talking."
- "(A foolproof method of producing an amusingly annoyed response from the distinguished experts? Just mention the word “ghosts.”) Whether they’re in on the joke or not doesn’t matter all that much."