Etymology
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boot camp (n.)

"training station for recruits," by 1941, U.S. Marines slang, said to be from boot (n.1) as slang for "recruit," which is attested by 1915 and supposedly dates from the Spanish-American War and is a synecdoche from boots "leggings worn by U.S. sailors."

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back up (v.)

1767, "stand behind and support," from back (v.) + up (adv.). The meaning "move or force backward" is by 1834. Of water prevented from flowing, by 1837.

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double date (n.)

"date involving two couples," by 1922, American English, from double (adj.) + date (n.3). As a verb by 1938. Related: Double-dating.

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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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air mail (n.)

also air-mail, airmail, 1913, from air (n.1) meaning "by aircraft" + mail (n.1). As a verb by 1919. Related: Air-mailed.

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toto caelo 

Latin, "by the whole heaven."

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per se 

"by himself, herself, or itself," 1570s, Latin, literally "by itself;" from per (see per) + se (see se-). The Latin phrase translates Greek kath auto (Aristotle).

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corn-row (n.)

also cornrow, 1769 as "a row of corn," by 1971 as a style of hair braids, so called for the resemblance. The verb in this sense also is by 1971.

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art brut (n.)

"art done by prisoners, lunatics, etc.," by 1948, as l'art brut, in a brief biography of Jean Dubuffet for Yale French Studies. French, literally "raw art" (see art (n.) + brute (adj.)).

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