old-fashioned slang A derogatory and offensive term for a psychiatric hospital or insane asylum. "Nut" is a derogatory slang term meaning "a crazy person." My great aunt Lidia apparently got locked up in a nuthouse when she was a teenager because she said she could commune with ghosts. I can't go to the police about it! They'd throw me in the nuthouse if I came to them with such an unbelievable story.