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Definition of lunacy

lunacy

/ˈluːnəsi/
lu · na · cy
Plural:lunacies
•
Adjective:lunatic
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lunacy Lexical Profile

lunacy Game Scores & Validity

• noun

1

Extreme folly, recklessness, or wildly irrational behavior.

Example

"Attempting to climb the mountain during a severe winter storm was sheer lunacy."

2

The state of being severely mentally ill or insane (now archaic in medical and legal usage, originally referring to intermittent madness believed to be caused by phases of the moon).

Example

"Nineteenth-century legal statutes often contained specific provisions regarding the property of individuals diagnosed with lunacy."

Synonyms
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Antonyms
View all antonyms for lunacy

Word Nuance & Usage

While historically used in legal and medical contexts to refer to severe mental illness, 'lunacy' is now outdated and inappropriate in clinical settings; in modern English, it is used almost exclusively to describe extreme foolishness or reckless behavior.

• Nearby Words

lumpsucker
lumpy
luna
lunacy
lunar
lunaria
lunatic

Word Origin & Etymology

Coined in the 16th century from the adjective 'lunatic', deriving from Late Latin 'lunaticus' ('moonstruck'), from Latin 'luna' ('moon'), reflecting the ancient belief that intermittent insanity was triggered by the phases of the moon.

Cite this Entry

Wordmom. (2026). Definition of Lunacy. In Wordmom Dictionary. Retrieved Nov 5, 2026, from https://wordmom.com/dictionary/lunacy
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