Etymology
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sleep (n.)

Old English slæp "sleep, sleepiness, inactivity," from Proto-Germanic *slepaz, from the root of sleep (v.); compare cognate Old Saxon slap, Old Frisian slep, Middle Dutch slæp, Dutch slaap, Old High German slaf, German Schlaf, Gothic sleps.

Personified in English from late 14c., on model of Latin Somnus, Greek Hypnos. Figurative use for "repose of death" was in Old English; to put (an animal) to sleep "kill painlessly" is recorded from 1923 (a similar imagery is in cemetery). Sleep deprivation attested from 1906. Sleep-walker "somnambulist" is attested from 1747; sleep-walking is from 1840. To be able to do something in (one's) sleep "easily" is recorded from 1953. Sleep apnea is by 1916.

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sleep (v.)

Old English slæpan "to be or fall asleep; be dormant or inactive" (class VII strong verb; past tense slep, past participle slæpen), from Proto-Germanic *slēpanan (source also of Old Saxon slapan, Old Frisian slepa, Middle Dutch slapen, Dutch slapen, Old High German slafen, German schlafen, Gothic slepan "to sleep"), from PIE *sleb- "to be weak, sleep," which perhaps is connected to PIE root *sleg- "be slack, be languid," the source of slack (adj.). Sleep with "do the sex act with" is in Old English:

Gif hwa fæmnan beswice unbeweddode, and hire mid slæpe ... [Laws of King Alfred, c. 900]

Related: Slept; sleeping. Sleep around is attested by 1928.

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CAT 
1975, medical acronym for computerized axial tomography or something like it. Related: CAT scan.
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cat (n.)

Old English catt (c. 700) "domestic cat," from West Germanic (c. 400-450), from Proto-Germanic *kattuz (source also of Old Frisian katte, Old Norse köttr, Dutch kat, Old High German kazza, German Katze), from Late Latin cattus.

The near-universal European word now, it appeared in Europe as Latin catta (Martial, c. 75 C.E.), Byzantine Greek katta (c. 350) and was in general use on the continent by c. 700, replacing Latin feles. Probably ultimately Afro-Asiatic (compare Nubian kadis, Berber kadiska, both meaning "cat"). Arabic qitt "tomcat" may be from the same source. Cats were domestic in Egypt from c. 2000 B.C.E., but not a familiar household animal to classical Greeks and Romans. The nine lives have been proverbial at least since 1560s.

The Late Latin word also is the source of Old Irish and Gaelic cat, Welsh kath, Breton kaz, Italian gatto, Spanish gato, French chat (12c.). Independent, but ultimately from the same source are words in the Slavic group: Old Church Slavonic kotuka, kotel'a, Bulgarian kotka, Russian koška, Polish kot, along with Lithuanian katė and non-Indo-European Finnish katti, which is from Lithuanian.

Extended to lions, tigers, etc. c. 1600. As a term of contempt for a woman, from early 13c. Slang sense of "prostitute" is from at least c. 1400. Slang sense of "fellow, guy," is from 1920, originally in African-American vernacular; narrower sense of "jazz enthusiast" is recorded from 1931.

Cat's paw (1769, but cat's foot in the same sense, 1590s) refers to the old folk tale in which the monkey tricks the cat into pawing chestnuts from a fire; the monkey gets the roasted nuts, the cat gets a burnt paw. Cat burglar is from 1907, so called for stealth. Cat-witted "small-minded, obstinate, and spiteful" (1670s) deserved to survive. For Cat's meow, cat's pajamas, see bee's knees. For let the cat out of the bag, see bag (n.).

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sleep-over (n.)
1935, from verbal phrase; see sleep (v.) + over (adv.).
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cat-head (n.)

"beam projecting from each side of the bows of a ship to hold the anchor away from the body of the ship," 1620s, from cat (n.) in some obscure sense.

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cat-lap (n.)

also catlap, "thin, poor beverage (especially weak tea)," 1785; see cat (n.) + lap (v.1). The notion is "fit only to give to cats."

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pussy-cat (n.)

also pussycat, "a cat," 1773, pleonastic, from pussy (n.1) + cat (n.). Applied to persons by 1859.

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kit-cat (n.)

name of a club founded by Whig politicians in London (Addison and Steele were members), 1703; so called from Christopher ("Kit") Catling, or a name similar to it, a tavernkeeper or pastry cook in London, in whose property the club first met. Hence "a size of portrait less than half length in which a hand may be shown" (1754), supposedly is because the dining room in which portraits of club members hung was too low for half-length portraits.

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cat-bath (n.)

"hurried or partial cleaning," 1935, from cat (n.) + bath (n.). Cat-lick in this sense is from 1892; Middle English had cat-likked "licked clean." 

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