The term non compos mentis comes from Latin, non meaning "not," compos meaning "in control," and mentis, genitive singular of mens, mind, and means not having a sound mind; not sane.

Although used in law, this term can be used metaphorically or figuratively. This entails when one is a confused state or state lacking rational thinking. If one is spaced out, one could claim that he or she is non compos mentis.

In English law, the rule of non compos mentis was most commonly used when the defendant invoked religious or magical explanations for behaviour.

Though authorities differ on this idea, the colloquial term nincompoop, meaning a stupid person, may be a distorted form of non compos mentis.

'Non Compos Mentis' is a segment on the FUEL TV show American Misfits featuring Pro Skateboarder Jason Jesse.

In Issac Asimov's Sucker Bait novella, the character Mark Annuncio uses the word 'noncompos' to insult persons outside of the Mnemonic Service. It is an abbreviation of the above phrase.

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