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

Keep scrolling for more

Examples of lunacy in a Sentence

Quitting her job was lunacy. His idea was considered total lunacy.
Recent Examples on the Web Someone had to begin to say no to the lunacy that has prevailed. Peter Georgescu For Cnn Business Perspectives, CNN, "While the government does nothing about gun violence, CEOs are filling the void," 10 Sep. 2019 Beyond the utter lunacy of the current college admission scandal is a much more widespread angst among parents and, increasingly, struggles among their kids. Ned Johnson, Washington Post, "College admissions scandal: Even if you could give your kid everything, should you?," 17 Sep. 2019 In the process, the lunacy of his theories might have been laid bare, and the Nazis who later used Stoddard and Grant and other American racists to justify the crimes of the Third Reich might have had less to work with. Ian Frazier, The New Yorker, "When W. E. B. Du Bois Made a Laughingstock of a White Supremacist," 19 Aug. 2019 The movie was made back when closing down several city blocks in San Francisco didn’t seem like sheer lunacy. Peter Hartlaub,, "The enduring appeal of ‘The Rock,’ beloved San Francisco film," 29 Aug. 2019 Looking back on the lunacy that was the beginning of ABC’s Monday Night Football, those garish yellow blazers worn by the broadcasters and pioneered by the Wide World of Sports crew were the least outrageous thing., "A History of Football in 100 Objects," 28 Aug. 2019 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

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.

See More

First Known Use of lunacy

1541, in the meaning defined at sense 1a

History and Etymology for lunacy


Keep scrolling for more

Learn More about lunacy

Statistics for lunacy

Last Updated

11 Nov 2019

Time Traveler for lunacy

The first known use of lunacy was in 1541

See more words from the same year

Keep scrolling for more

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

Keep scrolling for more

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).


to spread as a report or rumor

Get Word of the Day daily email!

Test Your Vocabulary

Confusing Words—A Quiz

  • alice with tweedle dee and tweedle dum
  • I invented a brand new toaster robot and ______ it "Sir Toasts-a-Lot."
Spell It

Can you spell these 10 commonly misspelled words?

Bee Cubed

Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!