Etymology
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cracked (adj.)

mid-15c., "broken by a sharp blow," past-participle adjective from crack (v.). From 1560s as "burst, split." Meaning "mentally unsound" is by 1690s. (compare crack-brain "crazy fellow"). The equivalent Greek word was used in this sense by Aristophanes.

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whack (v.)

"to strike sharply," 1719, probably of imitative origin. The noun is from 1737. The word in out of whack (1885) is perhaps the slang meaning "share, just portion" (1785), which may be from the notion of the blow that divides, or the rap of the auctioneer's hammer. To have (or take) a whack at something "make an attempt" is by 1820 (with have), 1845 (with take). Wack or whack "crazy person," 1938, is probably a back-formation from wacky, which probably comes from the blow-on-the-head verb. Related: Whacked; whacking. Whacked out is from 1969.

Wack, whack in the slang sense of "unappealing; crazy," hence "worthless, stupid" is by 1986, apparently popularized by an anti-drug slogan crack is wack.

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crackpot (n.)
"mentally unbalanced person," 1898, probably from crack (v.) + pot (n.1) in a slang sense of "head." Compare crack-brain "crazy fellow" (late 16c.). Earlier it was used in a slang sense "a small-time big-shot" (1883), and by medical doctors in reference to a "metallic chinking sometimes heard when percussion is made over a cavity which communicates with a bronchus."
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frenetic (adj.)

late 14c., frenetik, "temporarily deranged, delirious, crazed," from Old French frenetike "mad, crazy" (13c.), from Latin phreneticus "delirious," alteration of Greek phrenitikos, from phrenitis (nosos) "frenzy, mental disease, insanity," literally "inflammation of the brain," from phrēn "mind, reason," also "diaphragm" (see phreno-) + -itis "inflammation." The classical ph- sometimes was restored from mid-16c. (see phrenetic). Related: Frenetical; frenetically. Compare frantic.

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wild goose chase (n.)

"pursuit of anything in ignorance of the direction it will take," hence "a foolish enterprise," 1592, first attested in "Romeo and Juliet," where it evidently is a figurative use of an earlier (but unrecorded) literal sense in reference to a kind of follow-the-leader steeplechase, perhaps from one of the "crazy, silly" senses in goose (n.). Wild goose (as opposed to a domesticated one) is attested in late Old English (wilde gos).

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nuts (adj.)

"crazy, not right in the head," 1846, from earlier colloquial or slang be nuts on "be very fond of" (1785), which is possibly from nuts (plural noun) "any source of pleasure or delight" (1610s), from nut (q.v.). Nuts as a special treat or favorite foodstuff led to other figurative phrases, now obsolete. The "crazy" sense probably has been influenced by metaphoric application of nut to "head" (1846, as in to be off one's nut "be insane," 1860). Also compare nutty. Nuts as a derisive retort is attested from 1931.

Connection with the slang "testicles" sense has tended to nudge the word toward taboo territory. "On the N.B.C. network, it is forbidden to call any character a nut; you have to call him a screwball." [New Yorker, Dec. 23, 1950] "Please eliminate the expression 'nuts to you' from Egbert's speech." [Request from the Hays Office regarding the script of "The Bank Dick," 1940] This desire for avoidance probably accounts for the euphemism nerts (c. 1925).

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nutty (adj.)

early 15c., "nut-like," from nut (n.) + -y (2); from 1660s as "abounding in nuts." Sense of "having the flavor of nuts" is by 1828. Slang meaning "crazy" is by 1898 (see nuts); earlier colloquial sense was "amorous, in love (with)," 1821. [Byron, in a slangy passage in "Don Juan" (1823) uses it of a beggar's doxy; a footnote defines it as "conjointly, amorous and fascinating."] Related: Nuttiness.

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mental (adj.)

early 15c., "in, of, or pertaining to the mind; characteristic of the intellect," from Late Latin mentalis "of the mind," from Latin mens (genitive mentis) "mind," from PIE root *men- (1) "to think."

In Middle English, also "of the soul, spiritual." From 1520s as "done or performed in the mind." Meaning "crazy, deranged" is by 1927, probably from combinations such as mental patient (1859); mental hospital (1891). Mental health is attested by 1803; mental illness by 1819; mental retardation by 1904.

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nut (n.)

"the fruit of certain trees and shrubs which have the seed enclosed in a woody covering not opening when ripe," Middle English note, from Old English hnutu, from Proto-Germanic *hnut- (source also of Old Norse hnot, Dutch noot, Old High German hnuz, German Nuss "nut"), from PIE *kneu- "nut" (source also of Latin nux; see nucleus).

Sense of "testicle" is attested by 1915 (nuts). Nut-brown "brown as a ripe, dried nut" is from c. 1300 of animals; c. 1500 of complexions of women. The mechanical nut that goes onto a bolt is first recorded 1610s, from some fancied resemblance (nut was used of other small mechanical pieces since early 15c.). The figurative nuts and bolts "fundamentals" is by 1952. The American English slang sense of "amount of money required for something" is recorded by 1912.  

Meaning "crazy person, crank" is attested from 1903; British form nutter is attested by 1958. Nut-case "crazy person" is from 1959; nut-house "insane asylum" is by 1929. For more on this sense, see nuts. In slang, nut also meant "fashionable or showy young man of affected elegance" [OED], 1904.

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daffy (adj.)

"simple, wanting in intelligence," also "crazy, mad," 1884, perhaps from daft (adj.), or from obsolete daffe "a halfwit" (early 14c.; mid-13c. as a surname), which survived in 19c. in dialects, itself of uncertain origin (OED finds a proposed origin in Scandinavian words for "deaf, stupid," such as Old Norse daufr, "phonetically inadmissible"). Compare late 15c. daffish "dull-witted, spiritless." With -y (2). Related: Daffily; daffiness. The Warner Bros. cartoon character Daffy Duck debuted in 1937.

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