What word or phrase does your mother always say?
1940s slang, said to have originated in the U.S. military, perhaps from alleged sexual exploits of Hollywood actor Errol Flynn.
Accepted; acceptable; belonging to a select group; in: ''Are you in or out right now?'' ''I'm in like Flynn. Didn't you notice the picture on my desk?''
[1940s+, perhaps fr US Army Air Corps; origin uncertain; perhaps merely a rhyming phrase; perhaps associated with the sexual and other exploits of the actor Errol Flynn]