lunatic (n.) Look up lunatic at Dictionary.com
"lunatic person," late 14c., from lunatic (adj.).
lunatic (adj.) Look up lunatic at Dictionary.com
late 13c., "affected with periodic insanity, dependent on the changes of the moon," from Old French lunatique, lunage "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 seleniazomai "be epileptic," from selene "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 (1933) was Australian slang for "alcoholic drink."
lunacy (n.) Look up lunacy at Dictionary.com
1540s, "condition of being a lunatic," formed in English from lunatic + -cy. Originally in reference to intermittent periods of insanity, such as were believed to be triggered by the moon's cycle. The Old English equivalent was monaðseocnes "month-sickness."
insane (adj.) Look up insane at Dictionary.com
1550s, of persons, "mentally damaged," from Latin insanus "mad, insane, of unsound mind; outrageous, excessive, extravagant," from in- "not" (see in- (1)) + sanus "well, healthy, sane" (see sane). In reference to actions, "irrational, evidencing madness," from 1842 in English. The noun meaning "insane person" is attested from 1786. For the notion of insanity as sickness, compare lunatic; and Italian pazzo "insane," originally a euphemism, from Latin patiens "suffering." German verrückt, literally past participle of verrücken "to displace," "applied to the brain as to a clock that is 'out of order' " [Buck].
loony (adj.) Look up loony at Dictionary.com
also loonie, looney, 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 from 1919. 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.
idiot (n.) Look up idiot at Dictionary.com
early 14c., "person so mentally deficient as to be incapable of ordinary reasoning;" also in Middle English "simple man, uneducated person, layman" (late 14c.), from Old French idiote "uneducated or ignorant person" (12c.), from Latin idiota "ordinary person, layman; outsider," in Late Latin "uneducated or ignorant person," from Greek idiotes "layman, person lacking professional skill" (opposed to writer, soldier, skilled workman), literally "private person" (as opposed to one taking part in public affairs), used patronizingly for "ignorant person," from idios "one's own" (see idiom).

In plural, the Greek word could mean "one's own countrymen." In old English law, one who has been without reasoning or understanding from birth, as distinguished from a lunatic, who became that way. Idiot box "television set" is from 1959; idiot light "dashboard warning signal" is attested from 1961. Idiot savant attested by 1870.
fruitcake (n.) Look up fruitcake at Dictionary.com
also fruit-cake, 1838 in the literal sense "a rich, sweet cake containing fruit," from fruit + cake (n.). Slang meaning "lunatic person" is first attested 1952.
bedlam (n.) Look up bedlam at Dictionary.com
"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; converted to a state 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.
fantastic (adj.) Look up fantastic at Dictionary.com
late 14c., "existing only in imagination," from Middle French fantastique (14c.), from Medieval Latin fantasticus, from Late Latin phantasticus "imaginary," from Greek phantastikos "able to imagine," from phantazein "make visible" (middle voice phantazesthai "picture to oneself"); see phantasm. Trivial sense of "wonderful, marvelous" recorded by 1938. Old French had a different adjective form, fantasieus "weird; insane; make-believe." Medieval Latin also used fantasticus as a noun, "a lunatic," and Shakespeare and his contemporaries had it in Italian form fantastico "one who acts ridiculously."
off (adv.) Look up off at Dictionary.com
by c. 1200 as an emphatic form of Old English of (see of), employed in the adverbial use of that word. The prepositional meaning "away from" and the adjectival sense of "farther" were not firmly fixed in this variant until 17c., but once they were they left the original of with the transferred and weakened senses of the word. Meaning "not working" is from 1861. Off the cuff (1938) is from the notion of speaking from notes written in haste on one's shirt cuffs. Off the rack (adj.) is from 1963; off the record is from 1933; off the wall "crazy" is 1968, probably from the notion of a lunatic "bouncing off the walls" or else in reference to carom shots in squash, handball, etc.
moon (n.) Look up moon at Dictionary.com
Old English mona, from Proto-Germanic *menon- (source also of Old Saxon and Old High German mano, Old Frisian mona, Old Norse mani, Danish maane, Dutch maan, German Mond, Gothic mena "moon"), from PIE *me(n)ses- "moon, month" (source also of Sanskrit masah "moon, month;" Avestan ma, Persian mah, Armenian mis "month;" Greek mene "moon," men "month;" Latin mensis "month;" Old Church Slavonic meseci, Lithuanian menesis "moon, month;" Old Irish mi, Welsh mis, Breton miz "month"), probably from root *me- "to measure," in reference to the moon's phases as the measure of time.

A masculine noun in Old English. In Greek, Italic, Celtic, Armenian the cognate words now mean only "month." Greek selene (Lesbian selanna) is from selas "light, brightness (of heavenly bodies)." Old Norse also had tungl "moon," ("replacing mani in prose" - Buck), evidently an older Germanic word for "heavenly body," cognate with Gothic tuggl, Old English tungol "heavenly body, constellation," of unknown origin or connection. Hence Old Norse tunglfylling "lunation," tunglœrr "lunatic" (adj.).

Extended 1665 to satellites of other planets. To shoot the moon "leave without paying rent" is British slang from c. 1823; card-playing sense perhaps influenced by gambler's shoot the works (1922) "go for broke" in shooting dice. The moon race and the U.S. space program of the 1960s inspired a number of coinages, including, from those skeptical of the benefits to be gained, moondoggle (based on boondoggle). The man in the moon is mentioned since early 14c.; he carries a bundle of thorn-twigs and is accompanied by a dog. Some Japanese, however, see a rice-cake-making rabbit in the moon.
fool (n.1) Look up fool at Dictionary.com
early 13c., "silly, stupid, or ignorant person," from Old French fol "madman, insane person; idiot; rogue; jester," also "blacksmith's bellows," also an adjective meaning "mad, insane" (12c., Modern French fou), from Medieval Latin follus (adj.) "foolish," from Latin follis "bellows, leather bag" (see follicle).

The sense evolution probably is from Vulgar Latin use of follis in a sense of "windbag, empty-headed person." Compare also Sanskrit vatula- "insane," literally "windy, inflated with wind." But some sources suggest evolution from Latin folles "puffed cheeks" (of a buffoon), a secondary sense from plural of follis. One makes the "idiot" sense original, the other the "jester" sense.
The word has in mod.Eng. a much stronger sense than it had at an earlier period; it has now an implication of insulting contempt which does not in the same degree belong to any of its synonyms, or to the derivative foolish. [OED]
Also used in Middle English for "sinner, rascal, impious person" (late 13c.). Meaning "jester, court clown" in English is attested c. 1300, though it is not always possible to tell whether the reference is to a professional entertainer counterfeiting mental weakness or an amusing lunatic, and the notion of the fool sage whose sayings are ironically wise is also in English from c. 1300. The French word probably also got into English via its borrowing in the Scandinavian languages of the vikings (Old Norse fol, Old Danish fool, fol).
There is no foole to the olde foole ["Proverbs of John Heywood," 1546]
To make a fool of (someone) "cause to appear ridiculous" is from 1620s (make fool "to deceive, make (someone) appear a fool" is from early 15c.). Feast of Fools (early 14c., from Medieval Latin festum stultorum) was the burlesque festival celebrated in some churches on New Year's Day in medieval times. Fool's gold "iron pyrite" is from 1829. Fool's paradise "illusory state of happiness" is from mid-15c. Fool-trap is from 1690s. Foolosopher, a useful insult, is in a 1549 translation of Erasmus. Fool's ballocks is described in OED as "an old name" for the green-winged orchid. Fool-killer "imaginary personage invested with authority to put to death anybody notoriously guilty of great folly" is from 1851, American English.
Fool killer, a great American myth imagined by editors, who feign that his or its services are greatly needed, and frequently alluded to as being "around" or "in town" when some special act of folly calls for castigation. Whether the fool-killer be an individual or an instrument cannot always be gathered from the dark phraseology in which he or it is alluded to; but the weight of authority would sanction the impersonal interpretation. [Walsh, "Handy-Book of Literary Curiosities," 1892]