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lunacy

[loo-nuh-see] /ˈlu nə si/
noun, plural lunacies.
1.
insanity; mental disorder.
2.
intermittent insanity, formerly believed to be related to phases of the moon.
3.
extreme foolishness or an instance of it:
Her decision to resign was sheer lunacy.
4.
unsoundness of mind sufficient to incapacitate one for civil transactions: a former legal term.
Origin of lunacy
1535-1545
1535-45; lun(atic) + -acy
Synonyms
1. derangement, dementia; craziness, madness, mania, aberration. 3. folly, stupidity.
Antonyms
1, 2. rationality, sanity.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for lunacy

lunacy

/ˈluːnəsɪ/
noun (pl) -cies
1.
(formerly) any severe mental illness
2.
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
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Word Origin and History for lunacy
n.

1540s, "condition of being a lunatic," formed in English from lunatic + -cy. Originally in reference to intermittent periods of insanity, such as were believed to be triggered by the moon's cycle. The Old English equivalent was monaðseocnes "month-sickness."

Online Etymology Dictionary, © 2010 Douglas Harper
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