lunacy

noun

lu·​na·​cy ˈlü-nə-sē How to pronounce lunacy (audio)
plural lunacies
Synonyms of lunacynext
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

Synonyms of lunacy

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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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
After all, there’s ample lunacy to be found on the left and the right these days. — Clarence Page, Chicago Tribune, 30 Mar. 2026 Because it’s invariably attached to the idea of some kind of lunacy. — Zack Sharf, Variety, 3 Nov. 2025 Because it's invariably attached to the idea of some kind of lunacy. — Mekishana Pierre, Entertainment Weekly, 3 Nov. 2025 Once upon a time, the idea of a baseball team allowing most of its games to be broadcast on television was lunacy. — Ken Sugiura, AJC.com, 24 Feb. 2026 See All Example Sentences for lunacy

Word History

Etymology

lun(atic) + -acy

First Known Use

1541, in the meaning defined at sense 1a

Time Traveler
The first known use of lunacy was in 1541

Browse Nearby Words

luna
lunacy
luna moth
See all Nearby Words

Cite this Entry

“Lunacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/lunacy. Accessed 7 Jul. 2026.

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Kids Definition

lunacy

noun
lu·​na·​cy ˈlü-nə-sē How to pronounce lunacy (audio)
plural lunacies
: insanity sense 1
—used chiefly in the past

Medical Definition

lunacy

noun
lu·​na·​cy ˈlü-nə-sē How to pronounce lunacy (audio)
plural lunacies
dated
: mental illness
also : intermittent mental illness once believed to be related to phases of the moon

Legal Definition

More from Merriam-Webster on lunacy

Nglish: Translation of lunacy for Spanish Speakers

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