lunacy
Americannoun
-
lunacies
plural
-
insanity; mental disorder.
- Synonyms:
- aberration, mania, madness, craziness, dementia, derangement
- Antonyms:
- sanity, rationality
-
intermittent insanity, formerly believed to be related to phases of the moon.
- Antonyms:
- sanity, rationality
-
extreme foolishness or an instance of it.
Her decision to resign was sheer lunacy.
-
unsoundness of mind sufficient to incapacitate one for civil transactions: a former legal term.
noun
-
(formerly) any severe mental illness
-
foolishness or a foolish act
Other Word Forms
Noun Inflected Forms
Etymology
Origin of lunacy
Explanation
Lunacy is acting silly or stupid. Your mom might yell, "It's lunacy to go out in the snow wearing those flip flops!" Some people use the noun lunacy when they talk about actual mental instability, although this is considered old fashioned and outdated. It's much more common to describe the lunacy of someone who does something ridiculous or foolish. While adopting a cat from the animal shelter might be a great idea, adopting all thirty cats from the shelter would be lunacy. Lunacy comes from lunatic, originally "affected with periodic insanity, dependent on phases of the moon."
Vocabulary lists containing lunacy
Power Suffix: -acy
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And Then There Were None
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The Odyssey
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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.
See Examples For:
An obvious model for the film is “Babe,” but minus the droll wit, the inspired lunacy and the filigreed plot.
From The Wall Street Journal ● May 7, 2026
Beware the three Ls: leverage, liquidity and lunacy.
From MarketWatch ● Nov. 7, 2025
The company’s commedia dell’arte-style shenanigans have a natural elasticity but farcical lunacy snaps when stretched too far.
From Los Angeles Times ● Sep. 5, 2025
But Schaffer, Mand and Gregor are clearly graduates of the ZAZ school of punch-ups, and their ability to circle back toward police lunacy is classic “Naked Gun.”
From Salon ● Aug. 1, 2025
Private vigils held at night, made more private because they were expressions of public lunacy.
From "Song of Solomon" by Toni Morrison
Everyone knows why, another of the lunacies of the most lunatic sport.
From Washington Post ● Sep. 4, 2022
See also Gwyneth Paltrow, whose Goop website is always detailing madam’s various health issues, then trying to flog the fringe lunacies that presumably cause half of them.
From The Guardian ● Sep. 14, 2018
Their economic model combined the financial lunacies of Ireland and Iceland.
From The Guardian ● Sep. 22, 2010
Mr. O’Brien’s comic persona was always lighter and less intimate; he led a new breed of healthily irreverent comedians who mocked show business and its lunacies from the margins.
From New York Times ● Jun. 2, 2010
This should move us to be charitable towards one another's lunacies.
From Christian Science by Mark Twain
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.
