Etymology
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in vitro 

1892, scientific Latin; "in a test tube, culture dish, etc.;" literally "in glass," from Latin vitrum "glass" (see vitreous).

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alter ego (n.)

"second self, counterpart," 1530s, a Latin phrase (used by Cicero), "a second self, a trusted friend" (compare Greek allos ego); see alter and ego.

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wild man (n.)

c. 1200, "man lacking in self-restraint," from wild (adj.) + man (n.). From mid-13c. as "primitive, savage." Late 14c. as a surname.

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ipso facto 

Latin adverbial phrase, literally "by that very fact, by the fact itself," from neuter ablative of ipse "he, himself, self" + ablative of factum "fact" (see fact).

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Sinn Fein (n.)

1905, from Irish, literally "we ourselves," from Old Irish féin "self," from PIE *swei-no-, suffixed form of root *s(w)e- (see idiom). The movement was founded 1905 by Irish journalist and politician Arthur Griffith (1872-1922).

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cloud nine (n.)

by 1950, sometimes also cloud seven (1956, perhaps by confusion with seventh heaven), American English, of uncertain origin or significance. Some connect the phrase with the 1895 International Cloud-Atlas (Hildebrandsson, Riggenbach and Teisserenc de Bort), long the basic source for cloud shapes, in which, of the ten cloud types, cloud No. 9, cumulonimbus, was the biggest, puffiest, most comfortable-looking. Shipley suggests the sense in this and other expressions might be because, "As the largest one-figure integer, nine is sometimes used for emphasis." The phrase might appear in the 1935 aviation-based play "Ceiling Zero" by Frank Wilbur Wead.

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hat trick (n.)

in the sports sense, 1879, originally in cricket, "taking three wickets on three consecutive deliveries;" extended to other sports c. 1909, especially ice hockey ("In an earlier contest we had handed Army a 6-2 defeat at West Point as Billy Sloane performed hockey's spectacular 'hat trick' by scoring three goals" ["Princeton Alumni Weekly," Feb. 10, 1941]). So called allegedly because it entitled the bowler to receive a hat from his club commemorating the feat (or entitled him to pass the hat for a cash collection), but the term probably has been influenced by the image of a conjurer pulling objects from his hat (an act attested by 1876). The term was used earlier for a different sort of magic trick:

Place a glass of liquor on the table, put a hat over it, and say, "I will engage to drink every drop of that liquor, and yet I'll not touch the hat." You then get under the table; and after giving three knocks, you make a noise with your mouth, as if you were swallowing the liquor. Then, getting from under the table, say "Now, gentlemen, be pleased to look." Some one, eager to see if you have drunk the liquor, will raise the hat; when you instantly take the glass and swallow the contents, saying, "Gentlemen I have fulfilled my promise: you are all witnesses that I did not touch the hat." ["Wit and Wisdom," London, 1860]
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