c.1290, "affected with periodic insanity, dependent on the changes of the moon," from O.Fr. lunatique "insane," from L. lunaticus "moon-struck," from luna "moon." Cf. O.E. monseoc "lunatic," lit. "moon-sick;" M.H.G. lune "humor, temper, mood, whim, fancy" (Ger. Laune), from L. luna. Cf. also N.T. Gk. seleniazomai "be epileptic," from selene "moon." The noun meaning "lunatic person" is first recorded 1377. Lunatic fringe (1913) was apparently coined by U.S. politician Theodore Roosevelt. Lunatic soup (1933) was Australian slang for "alcoholic drink."
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.
Lu"na*tic\, a. [F. lunatique, L. lunaticus, fr. luna the moon. See Lunar.]1. Affected by lunacy; insane; mad. Lord, have mercy on my son; for he is lunatic. --Wyclif (Matt. xvii. 15). 2. Of or pertaining to, or suitable for, an insane person; evincing lunacy; as, lunatic gibberish; a lunatic asylum.