1541, "condition of being a lunatic," formed in Eng. from lunatic (q.v.). Originally in ref. to intermittent periods of insanity, such as were believed to be triggered by the moon's cycle. The O.E. equivalent was monaðseocnes "month-sickness."
Main Entry: lu·na·cy Pronunciation: 'lü-n&-sE Function: noun Inflected Form: plural-cies : any of various forms
of insanity: as a: intermittent insanity once believed to be related to phases of the moon b: insanity amounting to lack of capacity or of responsibility in the eyes
of the law
In*san"i*ty\, n. [L. insanitas unsoundness; cf. insania insanity, F. insanite.]1. The state of being insane; unsoundness or derangement of mind; madness; lunacy. All power of fancy overreason is a degree of insanity. --Johnson. Without grace The heart's insanity admits no cure. --Cowper. 2. (Law) Such a mental condition, as, either from the existence of delusions, or from incapacity to distinguish between right and wrong, with regard to any matter under action, does away with individual responsibility. Syn: Syn>- Insanity, Lunacy, Madness, Derangement, Aliention, Aberration, Mania, Delirium, Frenzy, Monomania, Dementia. Usage: Insanity is the generic term for all such diseases; lunacy has now an equal extent of meaning, though once used to denote periodical insanity; madness has the same extent, though originally referring to the rage created by the disease; derangement, alienation, are popular terms for insanity; delirium, mania, and frenzy denote excited states of the disease; dementia denotes the loss of mental power by this means; monomania is insanity upon a single subject.
Lu"na*cy\, n.; pl. Lunacies. [See Lunatic.]1. 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. --Brande. --Burrill. Your kindred shuns your house As beaten hence by your strange lunacy. --Shak. 2. A morbid suspension of good sense or judgment, as through fanaticism. --Dr. H. More. Syn: Derangement; craziness; mania. See Insanity.
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