Dictionary.com
Thesaurus.com
Synonyms

lunacy

American  
[loo-nuh-see] / ˈlu nə si /

noun

lunacies plural
  1. insanity; mental disorder.

    Synonyms:
    aberration, mania, madness, craziness, dementia, derangement
    Antonyms:
    sanity, rationality
  2. intermittent insanity, formerly believed to be related to phases of the moon.

    Antonyms:
    sanity, rationality
  3. extreme foolishness or an instance of it.

    Her decision to resign was sheer lunacy.

    Synonyms:
    stupidity, folly
  4. unsoundness of mind sufficient to incapacitate one for civil transactions: a former legal term.


lunacy British  
/ ˈluːnəsɪ /

noun

  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

Etymology

Origin of lunacy

First recorded in 1535–45; lun(atic) + -acy

Explanation

Lunacy is acting silly or stupid. Your mom might yell, "It's lunacy to go out in the snow wearing those flip flops!" Some people use the noun lunacy when they talk about actual mental instability, although this is considered old fashioned and outdated. It's much more common to describe the lunacy of someone who does something ridiculous or foolish. While adopting a cat from the animal shelter might be a great idea, adopting all thirty cats from the shelter would be lunacy. Lunacy comes from lunatic, originally "affected with periodic insanity, dependent on phases of the moon."

Keep Reading on Vocabulary.com

Vocabulary lists containing lunacy

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

“We don’t have anything like this in Vegas,” mused plus-size model and performer Alexandra Villalba, aka Lex Lunacy, who’d driven in from Sin City to make her Thick Strip debut.

From Los Angeles Times • Mar. 29, 2023

Many of its suggestions for the humane treatment and legal protection of the mentally ill were finally incorporated in the 1845 Lunacy Act.

From Nature • Apr. 4, 2017

But the lawyers declared, incorrectly, that the Lunacy Act did not cover mental disability.

From The Guardian • Nov. 9, 2012

Even before he midwifed the New Lunacy, Lardner was focusing at the flatlands of U.S. life a hard, unsparing look that went way beyond the familiar and funny.

From Time Magazine Archive

“With the breakdown of the Medieval system, the gods of Chaos, Lunacy, and Bad Taste gained ascendancy.”

From "A Confederacy of Dunces" by John Kennedy Toole

Vocabulary.com logo
by dictionary.com

Look it up. Learn it forever.

Remember "lunacy" for good with VocabTrainer. Expand your vocabulary effortlessly with personalized learning tools that adapt to your goals.

Take me to Vocabulary.com