lu·na·cy | \ˈlü-nə-sē \
plural lunacies

Definition of lunacy 

1 dated

a : insanity sense 1

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

Despite being an Arizona senator for the past 32 years, he’s done nothing to address the open-border lunacy and invasion that’s increased crime and strained the resources of his own state. Ed Stockly,, "Calendar Letters: Jane Pauley, John McCain, Roseanne Barr and more," 31 May 2018 Three centuries ago, notes the narrator— Willem Dafoe reading a text by the director and Robert Macfarlane —climbing a mountain would have been considered an act of lunacy. Joe Morgenstern, WSJ, "‘Mountain’ Review: Such Great Heights," 24 May 2018 The film’s thesis is that, until three centuries ago, it was deemed an act of lunacy to climb such a mountain. Peter Rainer, The Christian Science Monitor, "Documentary ‘Mountain’ has glorious panoramas," 1 June 2018 There are more than just a few Sapphic suggestions here, along with the religious lunacy, sadism, hallucinations, magic realism and a visual vocabulary rooted in horror. John Anderson, WSJ, "‘Picnic at Hanging Rock’ Review: No Walk in the Park," 24 May 2018 The influences of soul, rock, English folk, jazz, jug band and a heavy dose of industrial English LSD lunacy! Ron Hart, Billboard, "Small Faces' 'Ogdens' Nut Gone Flake' Turns 50: Phil Collen, Peter Frampton, Linda Thompson & More Pay Tribute," 24 May 2018 This is how hip-hop, the black intellectual scene, and our leadership eroded to the point of self-immolating lunacy. T.d. Williams, The Root, "How the West Was Lost," 26 Apr. 2018 Smith offers a welcomed happy medium between Johnson – who described himself as the dad driving a car filled with uncontrollable kids – and the lunacy of Chuck and Shaq’s rivalry. Michelle R. Martinelli, For The Win, "Dear Knicks: Please don't hire Kenny Smith, ruin best basketball show on TV," 20 Apr. 2018 The height of the evening's lunacy came when Jed Lowrie, battling Wilmer Font as if a playoff berth was on the line, capped an 11-pitch at-bat with a three-run homer in the ninth as the game approached the four-hour mark. Mike Digiovanna,, "Alex Wood is ineffective as Dodgers give up 21 hits in loss to Athletics," 12 Apr. 2018

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

30 Sep 2018

Look-up Popularity

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 \
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 \

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).


to reject or criticize sharply

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