lunatic
Americannoun
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(no longer in technical use; now considered offensive) an insane person.
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a person whose actions and manner are marked by extreme eccentricity or recklessness.
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a person legally declared to be of unsound mind and who therefore is not held capable or responsible before the law: a former legal term.
adjective
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(no longer in technical use; now considered offensive) insane.
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characteristic or suggestive of lunacy; wildly or recklessly foolish.
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Older Use. designated for or used by the insane.
a lunatic asylum.
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gaily or lightheartedly mad, frivolous, eccentric, etc..
She has a lunatic charm that is quite engaging.
adjective
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an archaic word for insane
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foolish; eccentric; crazy
noun
Other Word Forms
Etymology
Origin of lunatic
1250–1300; Middle English lunatik, from Old French lunatique, from Late Latin lūnāticus “moonstruck.” See Luna, -tic ( def. )
Explanation
A lunatic is someone who is either clinically insane or just acting really crazy. Someone driving too fast and zigging in and out of traffic is driving like a lunatic. The root of this word is luna, which means moon. That's because lunatic originally meant someone who went crazy with every phase of the moon, kind of like a werewolf. Most people these days don't believe in moon-caused insanity, but we still talk about lunatics, sometimes meaning clinically insane people. More often this is a slang term, used mainly in exaggerations, for anyone who seems wild and out of control.
Vocabulary lists containing lunatic
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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.
He got back everything he’s wanted and then a lunatic billionaire is telling you that 100 miles away under the Denver Airport there’s this thing that sounds crazy.
From Los Angeles Times • Mar. 30, 2026
That is a deliberate choice, says Tracy, because Teddy is not -- or at least not just -- a lunatic.
From Barron's • Mar. 1, 2026
“A lunatic was wildly screaming expletives in a complete fit of rage, and the president gave an appropriate and unambiguous response,” said Steven Cheung, White House communications director.
From The Wall Street Journal • Jan. 14, 2026
Social media can efficiently make any lunatic theory an ineradicable and ever-evolving virus.
From The Wall Street Journal • Jan. 9, 2026
His voice was thin, and he held his fierce lunatic head at an angle of bizarre arrogance.
From "The Left Hand of Darkness" by Ursula K. Le Guin
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
