also Q & A, 1954 (adj.), abbreviation of question and answer (itself attested by 1817 as a noun, by 1839 as an adjective).

drawn up 1867 by Sir John Sholto Douglas (1844-1900), 8th Marquis of Queensberry, to govern the sport of boxing in Great Britain.

"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-).

Quid pro quo, A terme among Apothecaries, when instead of one thing they use another of the same nature. [Cockeram, English Dictionarie, 1623]

1726, in on the qui vive "on the alert," from French être sur le qui vive "be on the alert," from the phrase qui voulez-vous qui vive? sentinel's challenge, "whom do you wish to live?" In other words "(long) live who?" meaning "whose side are you on?" (The answer might be Vive la France, Vive le roi, etc.). From qui (from Latin qui "who") + vive, third person singular present subjunctive of vivre, from Latin vivere "to live" (see viva).

mid-15c. (late 13c. in Anglo-French), "royal writ to determine by what warrant a person holds an office or franchise," a Medieval Latin legal phrase, literally "by what warrant," from quo "from, with, or by whom or what?," ablative of the interrogative pronoun quis "who?" (from PIE root *kwo-, stem of relative and interrogative pronouns). Also see warrant (n.).