Definitions

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

  • n. Insanity, especially insanity relieved intermittently by periods of clear-mindedness. See Synonyms at insanity.
  • n. Great or wild foolishness.
  • n. A wildly foolish act.
  • n. Archaic Intermittent mental derangement associated with the changing phases of the moon.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The state of being mad, insanity
  • n. Something deeply misguided.

from the GNU version of the Collaborative International Dictionary of English

  • n. 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.
  • n. A morbid suspension of good sense or judgment, as through fanaticism.

from The Century Dictionary and Cyclopedia

  • n. 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.
  • n. In law, unsoundness of mind sufficient to incapacitate for civil transactions. The usual test is incapacity to manage one's own property and affairs.
  • n. Synonyms Derangement, Craziness, etc. See insanity.

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

  • n. obsolete terms for legal insanity
  • n. foolish or senseless behavior

Etymologies

From lunatic.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From lunatic + -cy. (Wiktionary)

Examples

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