late 13c., "affected with periodic insanity dependent on the changes of the moon," from Old French lunatique "insane," or directly from Late Latin lunaticus "moon-struck," from Latin luna "moon" (see luna).
Compare Old English monseoc "lunatic," literally "moon-sick;" Middle High German lune "humor, temper, mood, whim, fancy" (German Laune), from Latin luna. Compare also New Testament Greek selēniazomai "be epileptic," from selēnē "moon." Lunatic fringe (1913) apparently was coined by U.S. politician Theodore Roosevelt.
Then, among the wise and high-minded people who in self-respecting and genuine fashion strive earnestly for peace, there are foolish fanatics always to be found in such a movement and always discrediting it — the men who form the lunatic fringe in all reform movements. [Theodore Roosevelt, autobiography, 1913].
Earlier it was a term for a type of hairstyle worn over the forehead (1877). Lunatic soup (1918) was slang for "alcoholic drink" or in reference to drinking several different alcoholic drinks together.
also loonie, looney, luny, "crazy; silly and eccentric," 1853, American English, short for lunatic, but also influenced by loon (n.2) and perhaps loon (n.1), the bird being noted for its wild cry and method of escaping from danger. As a noun by 1884, from the adjective.
Slang loony bin "insane asylum" is by 1909. Looney left in reference to holders of political views felt to be left-wing in the extreme is from 1977. Looney Tunes, Warner Bros. studios' animated cartoon series, dates from 1930.
Proto-Indo-European root meaning "light, brightness."
It forms all or part of: allumette; elucidate; illumination; illustration; lea; leukemia; leuko-; light (n.) "brightness, radiant energy;" lightning; limn; link (n.2) "torch of pitch, tow, etc.;" lucent; lucid; Lucifer; luciferase; luciferous; lucifugous; lucubrate; lucubration; luculent; lumen; Luminal; luminary; luminate; luminescence; luminous; luna; lunacy; lunar; Lunarian; lunate; lunation; lunatic; lune; lunette; luni-; luster; lustrum; lux; pellucid; sublunary; translucent.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit rocate "shines;" Armenian lois "light," lusin "moon;" Greek leukos "bright, shining, white;" Latin lucere "to shine," lux "light," lucidus "clear;" Old Church Slavonic luci "light;" Lithuanian laukas "pale;" Welsh llug "gleam, glimmer;" Old Irish loche "lightning," luchair "brightness;" Hittite lukezi "is bright;" Old English leht, leoht "light, daylight; spiritual illumination," German Licht, Gothic liuhaþ "light."
"scene of mad confusion," 1660s, from colloquial pronunciation of "Hospital of Saint Mary of Bethlehem" in London, founded 1247 as a priory, mentioned as a hospital 1330 and as a lunatic hospital 1402; it was converted to a civic lunatic asylum on dissolution of the monasteries in 1547. It was spelled Bedlem in a will from 1418, and Betleem is recorded as a spelling of Bethlehem in Judea from 971. The proper name might be caught in transition in the title of John Davies' 1617 publication of humorous poetry, "Wits bedlam —where is had, whipping-cheer, to cure the mad."