Meaning
Behave or think in a way the speaker considers eccentric, irrational, or mentally unsound. Informal and potentially offensive. It is often used as comic exaggeration about a reckless idea, but applying it to a person can stigmatize mental illness or eccentricity. Regional use: Widespread informal English.
Origin
The phrase is recorded from 1810. It compares a defect in a person's judgment with a machine or structure that does not work properly because a fastening is loose. Early 19th-century examples could refer broadly to something being wrong in a plan, case, or piece of machinery; the now familiar judgment about a person's mind became one established application of that wider metaphor. No particular machine, factory accident, or named speaker is known to have created it.
Research Sources
References used to check this entry’s meaning, history, or documented forms.
Variants
- Have a loose screw
- Have got a screw loose
Usage Examples
- Anyone who enters that cave during a flood must have a screw loose.
- The villagers think the clockmaker has a screw loose, but his calculations are exact.
- Saying that a patient has a screw loose replaces useful information with an insult.