lunatic

[ loo-nuh-tik ]
/ ˈlu nə tɪk /

noun

(no longer in technical use; now considered offensive) an insane person.
a person whose actions and manner are marked by extreme eccentricity or recklessness.
a person legally declared to be of unsound mind and who therefore is not held capable or responsible before the law: a former legal term.

adjective Also lu·nat·i·cal [loo-nat-i-kuh l] /luˈnæt ɪ kəl/ (for defs 4, 5, 7).

Origin of lunatic

1250–1300; Middle English lunatik, from Old French lunatique, from Late Latin lūnāticus “moonstruck.” See Luna, -tic
Related formslu·nat·i·cal·ly, adverbhalf-lu·na·tic, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for lunatic

British Dictionary definitions for lunatic

lunatic

/ (ˈluːnətɪk) /

adjective Also (rarely): lunatical (luːˈnætɪkəl)

an archaic word for insane
foolish; eccentric; crazy

noun

a person who is insane
Derived Formslunatically, adverb

Word Origin for lunatic

C13 (adj) via Old French from Late Latin lūnāticus crazy, moonstruck, from Latin lūna moon
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