have a screw loose


Be mentally unstable or eccentric, as in Anyone who approves that purchase must have a screw loose. This term likens a mental weakness to a machine in which a part is not securely fastened. An antonym is have one's head screwed on right; for example, She's very capable; she has her head screwed on right. [Slang; early 1800s]

Words Nearby have a screw loose

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.