lunacy

noun

lu·​na·​cy ˈlü-nə-sē 

plural lunacies

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

• absurdity
• asininity
• bêtise
• fatuity
• folly
• foolery
• foppery
• idiocy
• imbecility
• inanity
• insanity
• stupidity

Examples of lunacy in a Sentence

Quitting her job was lunacy.

His idea was considered total lunacy.

Recent Examples on the Web

How can Republicans in the Senate and Congress aid and abet this lunacy? —Sun Sentinel Editorial Board, Sun Sentinel, 6 Apr. 2025

Goggins is simply incredible, fully committed to Baby Billy’s comic lunacy yet never losing sight of his recovering sinner’s withered heart. —Ben Travers, IndieWire, 9 Mar. 2025

The public wants the economy humming, the border secure, and an end to woke lunacy — not tariffs and irrelevant indulgences. —Charles C. W. Cooke, National Review, 11 Mar. 2025

To suggest that anyone who vaccinates their kids doesn’t love them is a whole new level of lunacy. —Dr. Sanjay Gupta, CNN, 29 Jan. 2025

Word History

Etymology

lun(atic) + -acy

First Known Use

1541, in the meaning defined at sense 1a

Kids Definition

lunacy

noun

lu·​na·​cy ˈlü-nə-sē 

plural lunacies

: insanity sense 1

—used chiefly in the past

Medical Definition

lunacy

noun

lu·​na·​cy ˈlü-nə-sē 

plural lunacies

dated

: mental illness

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

Legal Definition

lunacy

noun

lu·​na·​cy ˈlü-nə-sē 

: insanity