lu·​na·​cy | \ ˈlü-nə-sē How to pronounce lunacy (audio) \
plural lunacies

Definition of lunacy

1 dated

b : intermittent insanity once believed to be related to phases of the moon
2 : wild foolishness : extravagant folly
3 : a foolish act

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Examples of lunacy in a Sentence

Quitting her job was lunacy. His idea was considered total lunacy.

Recent Examples on the Web

Astros insider: Home run derby in Oakland Oakland Coliseum created an environment on Thursday where such a thought was lunacy. Chandler Rome, Houston Chronicle, "Astros fall to Athletics in 10-homer slugfest," 16 Aug. 2019 Ditch conventional gear and use a fly rod, just to ramp up a challenging task to next-level lunacy. San Diego Union-Tribune, "Column: Toothy air show wows as local guide fly-fishes for mako sharks," 12 July 2019 Some admitted to their own moments of financial lunacy, such as running up credit card debt or falling for the extended warranty on the dishwasher. Susan Moeller,, "The 7 stupidest things we do with money," 13 June 2019 Merkley, a Democrat from Oregon, likes to recount the story to show the lunacy of the federal government’s treatment of the cannabis industry. Elizabeth Rembert,, "Bags stuffed with cash add to pressure for cannabis banking law," 8 Aug. 2019 In that context, giving up a Cy Young-caliber starter is the height of lunacy. Jon Tayler,, "Indians Come Out Surprisingly Well in Trevor Bauer Trade," 31 July 2019 The best time to catch all the lunacy is after local sunset on March 20 and 21, just as the moon rises. Andrew Fazekas, National Geographic, "See the first supermoon on the spring equinox in 19 years," 19 Mar. 2019 Of the 177 initial respondents, 62 percent said a morning kick was lunacy, compared to 38 percent in favor. Sean Keeler, The Denver Post, "Keeler: Larry Scott should spare CU Buffs from Pac-12’s Breakfast Club," 27 July 2019 In action, this summer 2019 game looks like the silly manipulate-anything concept of Job Simulator, only with an increased emphasis on smashy-smash lunacy that combines traditional weapons, supercharged implements of destruction, and everyday items. Sam Machkovech, Ars Technica, "E3’s first VR-exclusive gaming press conference was actually pretty rad," 10 June 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'lunacy.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of lunacy

1541, in the meaning defined at sense 1a

History and Etymology for lunacy


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Dictionary Entries near lunacy





luna moth

Luna Park


Statistics for lunacy

Last Updated

2 Sep 2019

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Time Traveler for lunacy

The first known use of lunacy was in 1541

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More Definitions for lunacy


lu·​na·​cy | \ ˈlü-nə-sē How to pronounce lunacy (audio) \
plural lunacies

Medical Definition of lunacy

: mental illness also : intermittent mental illness once believed to be related to phases of the moon


lu·​na·​cy | \ ˈlü-nə-sē How to pronounce lunacy (audio) \

Legal Definition of lunacy

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More from Merriam-Webster on lunacy

Thesaurus: All synonyms and antonyms for lunacy

Spanish Central: Translation of lunacy

Nglish: Translation of lunacy for Spanish Speakers

Britannica English: Translation of lunacy for Arabic Speakers

Comments on lunacy

What made you want to look up lunacy? Please tell us where you read or heard it (including the quote, if possible).


formidable, illustrious, or eminent

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