Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun Mental derangement; craziness.
  • noun Archaic Intermittent mental derangement attributed to the changing phases of the moon.
  • noun Great or wild foolishness.
  • noun A wildly foolish or irrational act.

from The Century Dictionary.

  • noun The kind of intermittent insanity formerly supposed to be subject to the change's of the moon; hence, madness in general; any unsoundness of mind. See insanity.
  • noun In law, unsoundness of mind sufficient to incapacitate for civil transactions. The usual test is incapacity to manage one's own property and affairs.
  • noun Synonyms Derangement, Craziness, etc. See insanity.

from the GNU version of the Collaborative International Dictionary of English.

  • noun Insanity or madness; properly, the kind of insanity which is broken by intervals of reason, -- formerly supposed to be influenced by the changes of the moon; any form of unsoundness of mind, except idiocy; mental derangement or alienation.
  • noun A morbid suspension of good sense or judgment, as through fanaticism.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun of a person or group of people The state of being mad, insanity
  • noun Something deeply misguided.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun obsolete terms for legal insanity
  • noun foolish or senseless behavior

Etymologies

from The American Heritage® Dictionary of the English Language, 4th Edition

[From lunatic.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From lunatic + -cy.

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