Online Etymology Dictionary

retroactive (adj.): 1610s, from French rétroactif (fem. rétroactive) "casting or relating back," from Latin retroactus, past participle of retroagere "drive or turn back," from retro- "back" (see retro-) + agere "to drive, set in motion" (see act).
retrofit: 1954, from retro(active) + (re)fit.
retroflex (adj.): 1776; , from Modern Latin retroflexus, past participle of retroflectere, from retro- (see retro-) + flectere "to bend" (see flexible). The verb (1898) is a back-formation from retroflexed (1806), from the adjective.
retrograde (adj.): late 14c., originally of the apparent motions of planets, from Latin retrogradus "going backward," from retrogradi "move backward," from retro- "backward" (see retro-) + gradi "to go, step" (see grade (n.)). General sense of "tending to revert" is recorded from 1530s.
retrogress (v.): 1819, from Latin retrogress-, past participle stem of retrogradi (see retrograde).
retrogression (n.): 1640s, formed on model of progression from Latin retrogressus, past participle of retrogradi "move backward" (see retrograde).
retrogressive (adj.): 1817; see retrogress + -ive. Related: Retrogressively.
retrospect: c.1600, from Latin retrospectum, past participle of retrospicere "look back," from retro- "back" (see retro-) + specere "look at" (see scope (n.1)).
retrospection (n.): 1630s, noun of action from Latin retrospicere (see retrospect).
retrospective (adj.): 1660s, from retrospect + -ive. As a noun, from 1964, short for retrospective exhibition (1919), etc. Related: Retrospectively.
retrovirus (n.): 1977, earlier retravirus (1974), from re(verse) tra(nscriptase) + virus. So called because it contains reverse transcriptase, an enzyme that uses RNA instead of DNA to encode genetic information, which reverses the usual pattern. Remodeled by influence of retro- "backwards."
return (v.): mid-14c., "to come back," from Old French retorner "turn back, return," from re- "back" (see re-) + torner "to turn" (see turn (v.)). Transitive sense is attested from early 15c. Related: Returned; returning.
return (n.): late 14c., "act of coming back," from Old French retorne from retorner (see return (v.)). 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.
Reuben: masc. proper name, Old Testament eldest son of Jacob and name of the tribe descended from him, from Greek Rouben, from Hebrew Reubhen, probably literally "Behold a son," from reu, imper. of ra'ah "he saw" + ben "a son." The reuben sandwich (1956) is "not obviously connected" with the sense in rube [OED].
reunification (n.): 1880; see re- + unification.
reunion (n.): c.1600, from re- "back, again" + union. Cf. French réunion (1540s). The island of Reunion, formerly known as Bourbon, was renamed during the French Revolution (1793) in commemoration of the 1792 union of revolutionaries from Marseille with the National Guard in Paris, renamed back to Bourbon after 1815, then back to the current name after 1848.
reunite (v.): 1590s, from adj. reunit "reunited" (mid-15c.), from Medieval Latin reunitus, past participle of reunire "unite again," from Latin re- "again" (see re-) + unire "join together" (see unite). Related: Reunited; reuniting.
reupholster (v.): 1935, see re- + upholster.
reuptake: by 1977; see re- + uptake.
reusable (adj.): 1959, first attested in a Sears, Roebuck & Co. catalogue (in reference to plastic bags for paper plates), from re- "back, again" + usable (see use (v.)).
reuse: 1843 (v.); 1866 (n.); see re- + use. Related: Reused; reusing.
Reuters: news service begun in London 1851 by Baron Paul Julius von Reuter (1816-1899), founder of a telegraph office and pigeon post bureau in Aachen in 1849.
rev (v.): 1916, from earlier noun (1901), shortening of revolution, in reference to the internal combustion engine. Related: Revved; revving.
revaluate (v.): 1949, back-formation from revaluation.
revaluation (n.): 1610s; see re- + valuation.
revamp (v.): 1850, from re- "again" + vamp "patch up, replace the upper front part of a shoe" (see vamp (v.)). An earlier verb was new-vamp (1630s).
revanche: 1858, from French revanche (see revanchist).
revanchist (n.): "one seeking to avenge Germany's defeat in World War I and recover lost territory," 1926 (on model of French revanchiste), from revanche "revenge, requital" (1858), especially in reference to a national policy seeking return of lost territory, from French revanche, literally "revenge," from Middle French revenche, back-formation from revenchier (see revenge).
reveal (v.): late 14c., from Old French reveler (14c.), from Latin revelare "reveal, uncover, disclose," literally "unveil," from re- "opposite of" (see re-) + velare "to cover, veil," from velum "a veil" (see veil (n.)). Revealed religion, as opposed to natural religion, is attested from 1719.
reveille: 1640s, from French réveillez (vous) "awaken!" imperative plural of réveiller "to awaken, to wake up," from Middle French re- "again" (see re-) + eveiller "to rouse," from Vulgar Latin *exvigilare, from Latin ex- "out" + vigilare "be awake, keep watch" (see vigil).
revel (n.): c.1300, "riotous merry-making," from Old French revel, from reveler "be disorderly, make merry," from Latin rebellare "to rebel" (see rebel). The verb meaning "to feast in a noisy manner" is first recorded early 14c. The meaning "take great pleasure in" first recorded 1754.
revelation (n.): c.1300, "disclosure of information to man by a divine or supernatural agency," from Old French revelacion, from Latin revelationem (nominative revelatio), from revelatus, past participle of revelare (see reveal). General meaning "disclosure of facts" is attested from late 14c.; meaning "striking disclosure" is from 1862. As the name of the last book of the New Testament (Revelation of St. John), it is first attested c.1400 (see apocalypse); as simply Revelations, it is first recorded 1690s.
revelatory (adj.): 1882; see revelation + -ory.
revelry (n.): "act of reveling," 15c.; see revel + -ery.
revenant: 1827, from French revenant, present participle of revenir "to return" (see revenue).
revenge (v.): late 14c., from Old French revengier, from re-, intensive prefix, + vengier "take revenge," from Latin vindicare "to lay claim to, avenge, punish" (see vindicate).
To avenge is "to get revenge" or "to take vengeance"; it suggests the administration of just punishment for a criminal or immoral act. Revenge seems to stress the idea of retaliation a bit more strongly and implies real hatred as its motivation. ["The Columbia Guide to Standard American English," 1993]
The noun is first recorded 1540s.
revengeful (adj.): 1580s; see revenge + -ful. Related: Revengefully.
revenue (n.): mid-15c., "income from property or possessions," from Middle French revenue, from Old French, "a return," prop. fem. past participle of revenir "come back," from Latin revenire "return, come back," from re- "back" (see re-) + venire "come" (see venue). Meaning "public income" is first recorded 1680s; revenue sharing popularized from 1971. Revenuer "U.S. Department of Revenue agent," the bane of Appalachian moonshiners, first attested 1880.
reverb (n.): 1961, colloquial shortening of reverberation.
reverberant: 1570s, from French réverbérant or directly from Latin reverberantem (nominative reverberans), present participle of reverberare (see reverberation).
reverberate (v.): 1570s, from Latin reverberatus, past participle of reverberare (see reverberation). Related: Reverberated; reverberating.
reverberation (n.): late 14c., "reflection of light or heat," from Old French reverberation, from Medieval Latin reverberationem (nominative reverberatio), noun of action from past participle stem of Latin reverberare "beat back," from re- "back" (see re-) + verberare "to strike, to beat," from verber "whip, lash, rod," related to verbena "leaves and branches of laurel," from PIE *werb- "to turn, bend" (see warp). Sense of "echo" is attested from 1620s.
revere (v.): 1660s, from French révérer, from Latin revereri (see reverence, which also was the earlier form of the verb). Related: Revered; revering.
reverence (n.): late 13c., from Old French reverence, from Latin reverentia "awe, respect," from revereri "to revere," from re-, intensive prefix, + vereri "stand in awe of, fear," from PIE *wer- "to be or become aware of" (cf. Old English wær "aware, cautious;" see wary). The verb is first attested c.1300.
reverend (adj.): early 15c., "worthy of respect," from Middle French reverend, from Latin reverendus "(he who is) to be respected," gerundive of revereri (see reverence). As a form of address for clergymen, it is attested from late 15c.; earlier reverent (late 14c. in this sense). Abbreviation Rev. is attested from 1721, earlier Revd. (1690s). Very Reverend is used of deans, Right Reverend of bishops, Most Reverend of archbishops.
reverent (adj.): late 15c., from Latin reverentem, present participle of revereri (see reverence). From 14c. through 17c., commonly also used for reverend (adj.). Related: Reverently.
reverential: 1550s, from Latin reverentia (see reverence) + -al (1). Related: Reverentially.
reverie (n.): mid-14c., "wild conduct, frolic," from Old French reverie "revelry, raving, delirium," from resver "to dream, wander, rave," of uncertain origin (also the root of rave). Meaning "daydream" is first attested 1650s. As a type of musical composition, it is attested from 1880.
reversal (n.): late 15c.; see reverse (v.) + -al (2).
reverse (adv./adj.): c.1300, from Old French revers "reverse, cross," from Latin reversus, past participle of revertere "turn back" (see revert). Reverse angle in film-making is from 1934. Reverse discrimination is attested from 1970 in a U.S. context (OED has a 1969 citation in reference to Northern Ireland).