"retreat, stop annoying someone," by 1938, from the verbal phrase, from back (v.) + off (adv.).

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.

c. 1600 (intransitive) "to return;" 1808 (transitive) "to recover (something);" from get (v.) + back.(adv.). Meaning "retaliate" is attested by 1888.

also back-seat, 1832, originally of coaches, from back (adj.) + seat (n.). Used figuratively for "less or least prominent position" by 1868. Back-seat driver "passenger who gives the driver unwanted advice" is attested by 1923.

You know him. The one who sits on the back seat and tells the driver what to do. He issues a lot of instructions, gives advice, offers no end of criticism and doesn't do a bit of work. ["The Back Seat Driver," Wisconsin Congregational Church Life, May 1923]

in figurative sense of "withdraw a charge," 1859, American English, from the notion of descending a ladder, etc. (such a literal sense is attested by 1849); from back (v.) + down (adv.).

"with the necessary changes," Latin, literally "things being changed that have to be changed," from the ablative plurals of, respectively, the past participle and gerundive of mutare "to change" (from PIE root *mei- (1) "to change, go, move").

1690s, French, "good-bye for now," literally "to the seeing again." From au "to the" (see au) + revoir "see again, see in turn" (Old French reveoir, 12c.), from Latin revidere, from re- "back, again" (see re-) + videre "to see" (see vision).

1620s, from Italian, literally "Frankish tongue." A stripped-down Italian peppered with Spanish, French, Greek, Arabic, and Turkish words, it began as a form of communication in the Levant. The name probably is from the Arabic custom, dating back to the Crusades, of calling all Europeans Franks (see Frank). In 17c. English sources also known as Bastard Spanish.

"dance by four couples placed opposite to each other and making the same steps and figures," 1803, from French contre-danse, altered from English country dance by folk etymology from French contra "against," suggested by the arrangement of the partners in the dance. The dances and the name were taken up in France c. 1720s and from there passed to Spain and Italy (Spanish, Italian contra danza) then back to English.

"lowest possible temperature which the nature of heat admits" (determined to be –273 centigrade, –458 Fahrenheit), the idea dates back to 1702 and its general value was guessed to within a few degrees soon thereafter, but not precisely discovered until Lord Kelvin's work in 1848. It was known by many names, such as infinite cold, absolute cold, natural zero of temperature; the term absolute zero was among them by 1806.