Etymology
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go for (v.)

1550s, "be taken or regarded as," also "be in favor of," from go (v.) + for (adv.). Meaning "attack, assail" is from 1880. Go for broke is from 1951, American English colloquial.

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tit for tat 

1550s, possibly an alteration of tip for tap "blow for blow," from tip (v.3) "tap" + tap "touch lightly." Perhaps influenced by tit (n.2).

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carry on (v.)

1640s, "continue to advance," also "manage, be engaged in," from carry (v.) + on (adv.). The meaning "conduct oneself in a wild and thoughtless manner" is by 1828. Carryings-on is from 1660s as "questionable doings," from 1866 as "riotous behavior." As an adjective, carry-on, in reference to luggage that may be brought into the passenger compartment of an airliner, is attested by 1965.

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pro bono 

short for Medieval Latin pro bono publico "for the public good;" from pro (prep.) "on behalf of, for" (see pro-) + ablative of bonum "good" (see bene-).

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raison d'etre (n.)

"excuse for being," 1864, first recorded in letter of J.S. Mill, from French raison d'être, literally "rational grounds for existence."

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pro tempore 

"temporary," Latin, literally "for the time (being)," from pro "for" (see pro-) + ablative singular of tempus "time" (see temporal). Abbreviated form pro tem is attested by 1828.

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quid pro quo 

"one thing in place of another," 1560s, from Latin, literally "something for something, one thing for another," from nominative (quid) and ablative (quo) neuter singulars of relative pronoun qui "who" (from PIE root *kwo-, stem of relative and interrogative pronouns) + pro "for" (see pro-).

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aqua fortis (n.)

also aquafortis, old commercial name for "diluted nitric acid," c. 1600, Latin, literally "strong water;" for the elements, see aqua- + fort. Also see aqua. So called for its power of dissolving metals (copper, silver) which are unaffected by other agents.

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g spot (n.)

also g-spot, 1981, short for Gräfenberg spot, named for German gynecologist Ernst Gräfenberg (1881-1957), who described it in 1950.

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a deux 

French, à deux, literally "for two," from à, from Latin ad "to, toward; for" (see ad-) + deux (see deuce). By 1876 as a French term in English.

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