[ loo-nuh-see ]
/ ˈlu nə si /

noun, plural lu·na·cies.

insanity; mental disorder.
intermittent insanity, formerly believed to be related to phases of the moon.
extreme foolishness or an instance of it: Her decision to resign was sheer lunacy.
unsoundness of mind sufficient to incapacitate one for civil transactions: a former legal term.

Origin of lunacy

First recorded in 1535–45; lun(atic) + -acy Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Examples from the Web for lunacy

British Dictionary definitions for lunacy

/ (ˈluːnəsɪ) /

noun plural -cies

(formerly) any severe mental illness
foolishness or a foolish act
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012