Online Etymology Dictionary

Reichstag (n.): "German imperial parliament" (1871-1918), earlier used of the chief deliberative body of the North German Confederacy, 1867, from German Reichstag, from Reich (see Reich) + Tag "assembly," literally "day" (see day). The Reichstag Fire was Feb. 27, 1933.
reification (n.): 1846, "act of materializing," from Latin re-, stem of res "thing" + -fication. In Marxist jargon, translating German Verdinglichung.
reify (v.): "make into a thing; make real or material; consider as a thing," 1854, back-formation from reification, or else from re-, stem of Latin res "thing, object; matter, affair, event; circumstance, condition," from PIE *re- "to bestow, endow" + -fy. Related: Reified; reifying.
reign (n.): early 13c., "kingdom," from Old French reigne "kingdom, land, country" (Modern French règne), from Latin regnum "kingship, dominion, rule, realm," related to regere "to rule, to direct, keep straight, guide" (see regal). Meaning "period of rule" first recorded mid-14c.
reign (v.): "to hold or exercise sovereign power," late 13c., from Old French regner "rule, reign" (12c.), from Latin regnare "have royal power, be king, rule, reign," from regnum "kingship, dominion, rule, realm," related to regere "to rule, to direct, keep straight, guide" (see regal). Related: Reigned; reigning; regnal.
reimburse (v.): 1610s, from re- "back" + imburse "to pay, enrich," literally "put in a purse" (c. 1530), from Middle French embourser, from Old French em- "in" + borser "to get money," from borse "purse," from Medieval Latin bursa (see purse (n.)). Related: Reimbursed; reimbursing.
reimbursement (n.): 1610s, from reimburse + -ment.
reimprison (v.): also re-imprison, 1610s, from re- + imprison. Related: Re-imprisoned; re-imprisoning.
Reims: city in northeastern France, named for the Remi, a Gaulish people whose name is said to mean "dominant ones." The former French spelling was with an Rh-.
rein (n.): c. 1300, "strap fastened to a bridle," from Old French rene, resne "reins, bridle strap, laces" (Modern French rêne), probably from Vulgar Latin *retina "a bond, check," back-formation from Latin retinere "hold back" (see retain). To give something free rein is originally of horses.
rein (v.): c. 1300, from rein (n.). Figurative extension "put a check on" first recorded 1580s. Related: Reined; reining. To rein up "halt" (1550s) is from the way to make a horse stop by pulling up on the reins.
reincarnate (v.): 1858, from re- + incarnate. Related: Reincarnated; reincarnating. As an adjective from 1882.
reincarnation (n.): 1829, "fact of repeated incarnation," from re- "back, again" + incarnation. Meaning "a new embodiment" is from 1854.
reindeer (n.): c. 1400, from a Scandinavian source such as Old Norse hreindyri "reindeer," from dyr "animal" (see deer) + hreinn, by itself the usual name for the animal, from Proto-Germanic *khrinda- (source also of Old English hran "reindeer;" German Renn "reindeer," which was altered by folk etymology influence of rennen "to run;" Swedish ren-ko "female reindeer," with ko "cow" (n.)).

Probably from PIE *krei-, from base *ker- (1) "horn, head," with derivatives referring to horned animals (both male and female reindeer have horns; those of the male are remarkable), and thus perhaps cognate with Greek krios "ram" (see kerato-). Older sources connect it to words in Lapp or Finnish. French renne, Spanish reno, Italian renna ultimately are from Germanic.
reinforce (v.): c. 1600, originally in military sense, from re- "again" + enforce (compare re-enforce). Related: Reinforced; reinforcing.
reinforcement (n.): c. 1600, "act of reinforcing," from reinforce + -ment. Meaning "an augmentation, that which reinforces" is from 1650s. Related: Reinforcements.
reins (n.): see rein (n.). Figurative sense "means of controlling; control, check, restraint" is from early 14c.
reinstall (v.): also re-install, 1590s, from re- + install. Related: Re-installed; re-installing.
reinstate (v.): 1590s, from re- + instate. Related: Reinstated; reinstating.
reinstatement (n.): 1700, from reinstate + -ment. Reinstation is recorded from 1680s.
reintegrate (v.): 1580s, from re- + integrate. Also in classically correct form redintegrate. Related: Reintegrated; reintegrating.
reintegration (n.): c. 1600, from French réintegration (15c.) or directly from Medieval Latin reintegrationem; see reintegrate + -ion. Also in classically correct form redintegration.
reintroduce (v.): 1660s, from re- + introduce. Related: Reintroduced; reintroducing.
reintroduction (n.): 1660s, from re- + introduction.
reinvent (v.): 1680s, from re- + invent. Related: Reinvented; reinventing. Phrase reinvent the wheel "do redundant work" attested by 1971.
reinvention (n.): 1719, from re- + invention.
reinvest (v.): 1610s, of money 1848, also re-invest, 1610s of vestments, etc.; 1848 of money; from re- + invest. Related: Reinvested; reinvesting.
reinvigorate (v.): 1650s, from re- + invigorate. Related: Reinvigorated; reinvigorating.
reinvite (v.): also re-invite, 1610s, from re- + invite (v.). Related: Reinvited; reinviting.
reissue (v.): 1610s, from re- "back, again" + issue (v.). Related: Reissued; reissuing. The noun is attested from 1805.
reiterate (v.): early 15c., "repeat again and again," from Late Latin reiteratus, past participle of reiterare "to repeat," from re- "again" (see re-) + iterare "to repeat," from iterum "again" (see iteration). Related: Reiterated; reiterating.
reiteration (n.): early 15c., from Middle French reiteration and directly from Latin reiterationem (nominative reiteratio) "repetition," noun of action from past participle stem of reiterare (see reiterate).
reject (v.): early 15c., from Old French rejecter and directly from Latin reiectus, past participle of reiectare "throw away, cast away, vomit," frequentative of reicere "to throw back," from re- "back" (see re-) + -icere, comb. form of iacere "to throw" (see jet (v.)). Related: Rejected; rejecting.
reject (n.): 1550s, "a castaway" (rare), from reject (v.). Modern use probably a re-formation of the same word: "thing cast aside as unsatisfactory" (1893); "person considered low-quality and worthless" (1925, from use in militaries).
rejection (n.): 1550s, from French réjection (16c.) or directly from Latin reiectionem (nominative reiectio) "act of throwing back," noun of action from past participle stem of reicere (see reject). In 19c., it also could mean "excrement." Medical transplant sense is from 1954. In the psychological sense, relating to parenting, from 1931.
rejoice (v.): c. 1300, "to own, possess, enjoy the possession of, have the fruition of," from Old French rejoiss-, present participle stem of rejoir, resjoir "gladden, rejoice," from re-, which here is of obscure signification, perhaps an intensive (see re-), + joir "be glad," from Latin gaudere "rejoice" (see joy).

Originally sense in to rejoice in. Meaning "to be full of joy" is recorded from late 14c. Middle English also used simple verb joy "to feel gladness; to rejoice" (mid-13c.) and rejoy (early 14c.). Related: Rejoiced; rejoicing.
rejoicing (n.): late 14c., verbal noun from rejoice (v.). Related: Rejoicingly.
rejoin (v.1): also re-join, 1520s, "unite again, unite after separation" (transitive), from re- "again" + join (v.). Meaning "join the company of again" is from 1610s. Related: Rejoined; rejoining.
rejoin (v.2): "to answer," mid-15c., legal term, from Middle French rejoin-, stem of rejoindre "to answer to a legal charge," from Old French re- "back" (see re-) + joindre "to join" (see join). General (non-legal) meaning first recorded 1630s.
rejoinder (n.): mid-15c., from Middle French noun use of rejoindre (see rejoin (v.2)). Originally "defendant's answer to the replication" (the fourth stage in the pleadings in an action at common law). For noun use of infinitive in French law terms, see waiver.
rejuvenate (v.): 1807, irregular formation from re- "again" + Latin juvenis "young" (see young (adj.)) + -ate (2). Related: Rejuvenated; rejuvenating.
rejuvenation (n.): 1834, noun of action from rejuvenate.
rejuvenescence (n.): "renewal of youth," 1630s, from Latin rejuvenescere, from re- "again" (see re-) + juvenescere "become young," from juvenis "young" (see young (adj.)) + -ence.
rejuvenescent (adj.): 1763, from Medieval Latin rejuvenescentem (nominative rejuvenescens), present participle of rejuvenescere (see rejuvenescence).
rekindle (v.): 1590s, from re- "back, again" + kindle (v.). Figurative use from 1650s. Related: Rekindled; rekindling.
relapse (v.): early 15c., "renounce;" 1560s, "fall into a former state," from Latin relapsus, past participle of relabi "slip back, slide back, sink back," from re- "back" (see re-) + labi "to slip" (see lapse (n.)). Related: Relapsed; relapsing.
relapse (n.): mid-15c., from relapse (v.).
relate (v.): 1520s, "to recount, tell," from Middle French relater "refer, report" (14c.) and directly from Latin relatus, used as past participle of referre "bring back, bear back" (see refer), from re- "back, again" + latus (see oblate (n.)).

Meaning "stand in some relation; have reference or respect" is from 1640s; transitive sense of "bring (something) into relation with (something else)" is from 1690s. Meaning "to establish a relation between" is from 1771. Sense of "to feel connected or sympathetic to" is attested from 1950, originally in psychology jargon. Related: Related; relating.
related (adj.): "connected by blood or marriage," 1702, past participle adjective from relate (v.). Related: Relatedness.
relation (n.): late 14c., "connection, correspondence;" also "act of telling," from Anglo-French relacioun, Old French relacion "report, connection" (14c.), from Latin relationem (nominative relatio) "a bringing back, restoring; a report, proposition," from relatus (see relate). Meaning "person related by blood or marriage" first attested c. 1500. Stand-alone phrase no relation "not in the same family" is attested by 1930.