Online Etymology Dictionary

back (adj.): O.E. bæc "backwards, behind" (see back (n.)). Back-seat driver first attested 1926. The back of (one's) hand has been used to imply contempt and rejection since at least 1300; to know (something) like the back of one's hand, implying familiarity, is first attested 1943. To be on the back burner in the figurative sense is from 1960, from the image of a cook keeping a pot there to simmer while he or she works on another concoction at the front of the stove. Back-to-nature (adj.) is first attested 1915.
back (v.): late 15c., "to move (something) back," from back (adj.); meaning "to support" (as by a bet) is first attested 1540s.
back (n.): O.E. bæc "back, backwards, behind," from P.Gmc. *bakam (cf. O.S., M.Du. bak, O.Fris. bek), with no known connections outside Germanic. The cognates mostly have been ousted in this sense in other modern Gmc. languages by words akin to Modern English ridge (cf. Dan. ryg, Ger. Rücken). Many I.E. languages show signs of once having distinguished the horizontal back of an animal (or a mountain range) from the upright back of a human. In other cases, a modern word for "back" may come from a word related to "spine" (It. schiena, Rus. spina) or "shoulder, shoulder blade" (Sp. espalda, Pol. plecy).
backlog: 1680s, from back + log. Originally a large log placed at the back of a fire. Figurative sense is first attested 1883, via notion of "a reserve of something stored up."
back-formation: coined c.1890s by Eng. lexicographer James Murray (1837-1915) from back (adj.) + noun of condition from form (q.v.).
back down: in fig. sense of "withdraw a charge," 1859, Amer.Eng., from notion of descending a ladder, etc.; from back (v.) + down (adv.).
back up (v.): 1767, "stand behind and support," from back (v.) + up. The noun meaning "standby, reserve" is recorded from 1952 (often written as one word, backup); specific reference to computing is from 1965.
back-talk: "impertinent retort," 1858, originally often used in literary attempts at low Irish idiom, from back (adj.) + talk.
backdoor: "devious, shady, illegal," 1640s, from back + door. The notion is of business done out of public view. The association with sodomy is at least from 19c.; also back-door man "a married woman's lover," black slang, early 20c.
back off (v.): "retreat, stop annoying someone," by 1938, from back (v.) + off.
backfire: 1839, Amer.Eng., originally "a fire deliberately lit ahead of an advancing prairie fire to deprive it of fuel," from back + fire (v.). As a verb in this sense, recorded from 1886. The meaning "premature ignition in an internal-combustion engine" is first recorded 1897. Of schemes, plans, etc., "affect the initiator rather than the intended object" it is attested from 1912, a fig. use from the accidental back-firing of firearms.
backup: see back up.
backing: 1590s, "support;" 1640s, "retreat;" from back (v.). Physical sense of "anything forming a backing to something else" is from 1793. Meaning "musical accompaniment" is recorded from 1940.
backbencher: 1874 in the House of Commons sense, from back (adj.) + bench, occupants of the rear seats being the least-prominent politicians.
backbone: "spine," c.1300, from back (n.) + bone. Fig. sense of "strength of character" is attested from 1843.
backside: late 15c., from back (adj.) + side. In the specific sense of "rump, buttocks" it is first recorded c.1500.
backlash: 1815, of machinery, from back (adj.) + lash. In metaphoric sense, it is attested from 1921.
backslash: 1982, new punctuation symbol introduced for computer purposes, from back (adj.) + slash (n.).
backhand: as a tennis stroke, 1650s, from back (adj.) + hand. The fig. sense of "indirect" is from c.1800.
backpack: 1914 as a noun, 1916 as a verb, from back + pack.
backtrack: "retrace one's steps," 1904, from back (adj.) + track (v.).
backwash: 1876, Motion of a receeding wave," from back + wash.
backstop (n.): 1819, in cricket, from back + stop. In U.S. baseball, from 1889; fig. extension to "catcher on a baseball team" is from 1890. The verb is attested from 1956 in the sense of "support."
background: 1670s, from back (adj.) + ground; original sense was theatrical, later applied to painting. Figurative sense is first attested 1854.
backdrop: 1913, in U.S. theatrical argot, from back + drop.
backslide: in the religious sense, 1580s, from back (adj.) + slide.
backfill (n.): 1901 (as backfilling), from back (adj.) + fill (n.). The verb was in use by 1930.
backyard: 1650s, from back (adj.) + yard (1).
backwater: late 14c., "water behind a dam," from back + water. Hence flat water without a current near a flowing river, as in a mill race (1820); fig. use of this for any flat, dull place is from 1899.
backstabber: in the fig. sense is from 1906, from back (n.) + stab. Originally in ref. to politicians and the working class in England. The verb backstab in the fig. sense is from 1925.
backbiting: late 12c., bacbitunge, from back (adj. or n.) + biting.
backhoe: by 1928, from back + hoe.
backgammon: 1640s, baggammon, the second element from M.E. gamen, ancestor of Mod.E. game; the first element because pieces are sometimes forced to go "back." Known 13c.-17c. as tables.
backdate: 1946, from back (adj.) + date. Cf. antedate.
recoil (v.): early 13c., "force back," from O.Fr. reculer "to go back, recede, retreat," from V.L. *reculare, from L. re- "back" + culus "backside." Meaning "shrink back" is first recorded 1510s, and that of "spring back" (as a gun) in 1520s. The noun is attested from early 14c.
refund (v.): "to give back, restore," early 15c. (earlier "to pour back," late 14c.), from O.Fr. refunder "restore," from L. refundere "give back, restore," lit. "pour back," from re- "back" + fundere "to pour" (see found (2)). Specifically of money from 1550s. The noun is 1866, from the verb.
outback: "back-country, interior regions of Australia," 1907, Australian Eng., originally an adv., "out in the back settlements" (1878), from out + back.
dossier: 1880, from Fr. dossier "bundle of papers," from dos "back," supposedly because the bundle bore a label on the back, from L. dossum, var. of dorsum "back." Or possibly from resemblance of the bulge in a mass of bundled papers to the curve of a back.
re-: prefix meaning "back to the original place, again," also with a sense of "undoing," c.1200, from O.Fr. and directly from L. re- "again, back, against." Often merely intensive.
recidivist: 1880, "relapsed criminal," from Fr. récidiviste, from récidiver "to fall back, relapse," from M.L. recidivare "to relapse into sin," from L. recidivus "falling back," from recidere "fall back," from re- "back, again" + comb. form of caedere "to fall" (see concise). Recidivation in the spiritual sense is attested from c.1420, was very common 17c.
decriminalize: 1963, "to reform a criminal," back-formation from decriminalization. Meaning "to make legal something that formerly had been illegal" was in use by 1970 (there are isolated instances back to 1867).
return: mid-14c., "to come back," from O.Fr. retorner "turn back, return," from re- "back" + torner "to turn" (see turn). Transitive sense is attested from early 15c. The noun is first attested late 14c., "act of coming back;" in the tennis sense, it is from 1886. Meaning "official report of election results" is attested from mid-15c. Meaning "a yield, a profit" is recorded from 1620s. Many happy returns of the day was used by Addison, 1716.
reprieve (v.): 1571, "take back to prison," from M.E. repryen "to remand, detain" (1494), probably from M.Fr. repris, pp. of reprendre "take back" (see reprise). Meaning "to suspend an impending execution" is recorded from 1596. Sense evolved because being sent back to prison was the alternative to being executed. The noun is first attested 1598.
do-si-do: 1929, from Fr. dos-à-dos "back to back."
anapest: 1670s, "two short syllables followed by a long one," from L. anapestus, from Gk. anapaistos "struck back, rebounding," verbal adj. from anapaiein "to strike back," from ana- "back" + paiein "to strike;" so called because it reverses the dactyl.
anaphora: repetition of a word or phrase in successive clauses, 1580s, from L., from Gk. anaphora "a carrying back," from anapherein "to carry back," ana "back" + pherein "to bear" (see infer).
reserve (v.): mid-14c., from O.Fr. reserver, from L. reservare "keep back, save back," from re- "back" + servare "to keep, save, preserve, protect" (see observe). The noun meaning "something stored up" is from 1650s. Reserved (in manner) first recorded 1601 in Shakespeare ("All's Well" v.3).
refer: late 14c., "to trace back, attribute, assign," from O.Fr. referer (14c.), from L. referre "to relate, refer," lit. "to carry back," from re- "back" + ferre "carry" (see infer). Meaning "to commit to some authority for a decision" is from mid-15c.; sense of "to direct (someone) to a book, etc." is from c.1600.
slum: 1845, from back slum "back alley, street of poor people" (1825), originally a slang word meaning "room," especially "back room" (1812), of unknown origin. Go slumming is from 1884, pastime popularized by East End novels. Slumlord first attested 1953, from slum landlord (1893).
reflection: late 14c., in reference to surfaces, from L.L. reflexionem (nom. reflexio) "a reflection," lit. "a bending back," from L. reflex-, pp. stem of reflectere, from re- "back" + flectere "to bend." Meaning "remark made after turning back one's thought on some subject" is from 1650s.