Synonyms

insane

American

[in-seyn] / ɪnˈseɪn /

adjective

(not in technical use as a medical diagnosis) not sane; not of sound mind; mentally deranged.

Synonyms:

irrational, foolish, maniacal, crazy, crazed, lunatic, demented
of, relating to, or characteristic of a person who is mentally deranged.

a wild and insane look on her face.
Law. considered to be or to have been affected with insanity, and therefore lacking legal responsibility or legal capacity.

The judge deemed him criminally insane on the basis of his delusions and hallucinations.
temporarily unable to think clearly.

I think I'm going insane from all the noise outside.
utterly senseless.

an insane plan.
Slang. excessive or extravagant; extreme.

This much snow in April is just insane!
Slang. astonishingly great; wonderful.

Without his insane performance, the film would've been a total flop.

insane British

/ ɪnˈseɪn /

adjective

1. mentally deranged; crazy; of unsound mind
2. ( as collective noun; preceded by the )
  
  the insane
characteristic of a person of unsound mind

an insane stare
irresponsible; very foolish; stupid

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Related Words

See mad.

Other Word Forms

insanely adverb
insaneness noun
pseudoinsane adjective

Etymology

Origin of insane

First recorded in 1550–60; from Latin insānus “unsound (of mind), demented, frenzied”; in- ³, sane

Explanation

To be insane is to have a seriously disordered state of mind. This is also a slang word for acting wacky or wild. This word has two closely related meanings. People who are insane are suffering from a seriously irrational or disordered state of mind. When someone commits a crime, it's important to know if they were sane or insane. If they're insane, the penalty is different. Many uses of the word are not so serious. A wild party is called insane, and car salesmen say their prices are insane. A teacher assigning six hours of homework might be told "That’s insane!"

Keep Reading on Vocabulary.com

Vocabulary lists containing insane

salu, san (health)

Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

But they were also about to prove that they were already better than most humans at making sense of a tournament known for being completely insane, as Ben Cohen and Andrew Beaton write.

From The Wall Street Journal • Mar. 28, 2026

And the core of that story, a man falsely imprisoned for a crime he didn’t commit and eventually driving him insane, is unfortunately pretty evergreen.

From Los Angeles Times • Mar. 19, 2026

Another added: "It would be insane to challenge the patient."

From BBC • Mar. 11, 2026

When the Islamic revolution happened in 1979, they said, This is an insane system, a monarchy, that the son of the current guy is the person who’s going to rule until he dies.

From Slate • Mar. 11, 2026

“But I’d still like to know how we make our way through the House of Hades without going insane or dying.”

From "The House of Hades" by Rick Riordan

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023