nutter

Nutter is a colloquial term used primarily in English-speaking regions to describe a person perceived as mentally unstable or extremely eccentric. In casual speech it can function as a mild insult or a humorous nickname, but it may be offensive depending on context and intent.

The etymology traces to nut, a slang reference to the head or mind, with the sense of "crazy" appearing in British English in the 20th century and spreading to other varieties of English. As a result, "nutter" is typically informal and regional rather than a formal psychiatric term.

Nutter is also a surname of English origin. People with this surname have appeared in historical records and modern public life across various fields, including politics, academia, and the arts. In this sense, the word is not a descriptor of a condition but a family name.

In popular culture and media, nutter is used as a colloquial descriptor for characters or behavior that is unusual or irrational. The term's tone can range from affectionate to pejorative, depending on the speaker and audience.