Online Etymology Dictionary

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 rejoindre (see rejoin (v.2)). Originally "defendant's answer to the replication."
rejuvenate (v.): 1807, from re- "again" + Latin juvenis (see young) + -ate (2). Related: Rejuvenated; rejuvenating. Noun rejuvensecence "renewal of youth" is first recorded 1631.
rekindle (v.): 1590s, from re- "back, again" + kindle (v.). Related: Rekindled; rekindling.
relapse (v.): 1560s, from Latin relapsus, past participle of relabi "slip back," from re- "back" (see re-) + labi "to slip" (see lapse (n.)). Related: Relapsed; relapsing. The noun is first attested 1530s.
relate (v.): 1530, "to recount, tell," from Latin relatus, used as past participle of referre (see refer), from re- "back, again" + latus (see oblate (n.)). 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 in the sense of "connected by blood or marriage" is from 1702.
relation (n.): late 14c., from Anglo-French relacioun, Old French relacion (14c.), from Latin relationem (nominative relatio) "a bringing back, restoring," 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.
relational (adj.): 1660s, from relation + -al (1).
relationship (n.): 1744, "sense of being related," from relation + -ship. Specifically of romantic or sexual relationships by 1944.
relative (n.): late 14c., "a relative pronoun," from Old French relatif (13c.), from Late Latin relativus "having reference or relation," from Latin relatus, past participle of referre "to refer" (see refer). Meaning "person in the same family" first recorded 1650s; the adjective is attested from 1520s.
relatively (adv.): "in relation to something else," 1560s, from relative + -ly (2).
relativism (n.): 1865, in philosophy, from relative (adj.) + -ism. Cf. relativist.
relativist (n.): 1857, from relative + -ist. As an adjective from 1914. Related: Relativistic.
relativity (n.): 1834, "fact or condition of being relative," from relative (adj.) (see relative (n.)); first attested in Coleridge. In scientific use, connected to the theory of Albert Einstein (1879-1955), published 1905 (special theory of relativity) and 1915 (general theory of relativity), but the word was used in roughly this sense by J.C. Maxwell in 1876.
relator (n.): "informer," c.1600, from Latin relator, agent noun; see relate.
relaunch (v.): 1745, from re- + launch. Related: Relaunched; relaunching. As a noun from 1970.
relax (v.): early 15c., "to make (something) less compact or dense," from Old French relaxer (14c.), from Latin relaxare "relax, loosen, open," from re- "back" (see re-) + laxare "loosen," from laxus "loose" (see lax). Of persons, attested from 1837, "to become less formal;" meaning "to become less tense" is recorded from 1935. Related: Relaxed; relaxing.
relaxation (n.): 1520s, "remission of a burden or penalty," Latin relaxationem (nominative relaxatio), noun of action from past participle stem of relaxare (see relax). Meaning "relief from hard work or ordinary cares" is from 1540s.
relay (n.): late 14c., "hounds placed along a line of chase," from Middle French relai "reserve pack of hounds or other animals" (13c.), from Old French relaier "to exchange tired animals for fresh," literally "leave behind," from re- "back" (see re-) + laier "to leave" (see delay). The etymological sense is "to leave (dogs) behind (in order to take fresh ones)." Of horses, 1650s. Electromagnetic sense first recorded 1860. As a type of foot-race, it is attested from 1898.
relay (v.): c.1400, "to set a pack of (fresh) hounds after a quarry," from Old French relaiier, from relai (see relay (n.)). Related: Relayed; relaying.
release (v.): c.1300, "to withdraw, revoke," also "to liberate" (c.1300), from Old French relaisser "to relinquish, quit, let go, leave behind," variant of relacher "release, relax," from Latin relaxare (see relax). Meaning "relinquish, surrender" is recorded from late 14c. Of press reports, attested from 1904; of motion pictures, from 1912; of music recordings, from 1962. As a euphemism for "to dismiss, fire from a job" it is attested in American English since 1904. Related: Released; releasing.
release (n.): early 14c., from Old French reles (12c.), a back-formation from relesser, relaisser (see release (v.)).
relegate (v.): 1580s "to banish, send into exile" (implied in relegation), from Latin relegatus, past participle of relegare "remove, dismiss, banish," from re- "back" + legare "send with a commission" (see legate). Meaning "place in a position of inferiority" is recorded from 1790. Related: Relegated; relegating.
relent (v.): late 14c., "to melt, soften, dissolve," from re-, intensive prefix, + Latin lentus "slow, viscous, supple" (see lithe). Sense of "become less harsh or cruel" first recorded 1520s. The notion probably is of a hard heart melting with pity. Related: Relented; relenting.
relentless (adj.): 1590s, from relent + -less. Related: Relentlessly; relentlessness.
relevant (adj.): "pertinent to the matter at hand," 1550s, from Medieval Latin relevantem (late 15c.), present participle of Latin relevare "to lessen, lighten" (see relieve). Originally a Scottish legal term meaning "take up, take possession of property;" not generally used until after 1800. Relevance is from 1733 (relevancy in the same sense is recorded from 1560s).
releve (n.): 1825 as a dish; 1930 in ballet, from French relevé, literally "raised up."
reliable (adj.): 1560s, raliabill, Scottish; see rely + -able. Not common before 1850; and execrated thereafter in Britain as an Americanism. Related: Reliably; reliability.
reliance (n.): c.1600; see rely + -ance.
reliant (adj.): 1856; see rely + -ant. Because it means "dependent (on)" it would seem an odd name for an automobile, but Chrysler (Plymouth) nonetheless chose it as one in 1981.
relic (n.): early 13c., "body part or other object from a holy person," from Old French relique (11c.), from Late Latin reliquiæ (plural) "remains of a martyr," in classical Latin "remains, remnants," noun use of fem. plural of reliquus "remaining, that which remains," from re- "back" + root of linquere "to leave" (see relinquish). Sense of "remains, ruins" is from early 14c. Old English used reliquias, directly from Latin.
relict (adj.): "widow," mid-15c., from Medieval Latin relicta "widow," noun use of fem. of relictus "abandoned, left behind," properly past participle of Latin relinquere "to leave behind" (see relinquish).
relief (n.1): "ease, alleviation," early 14c., from Anglo-French relif, from Old French relief "assistance," literally "a raising, that which is lifted," from stressed stem of relever (see relieve). Meaning "aid to impoverished persons" is attested from c.1400; that of "deliverance of a besieged town" is from 1540s.
relief (n.2): "projection of figure or design from a flat surface," c.1600, from Italian rilievo, from rilevare "to raise," from Latin relevare "to raise, lighten" (see relieve).
relieve (v.): c.1300, from Old French relever "to raise, relieve" (11c.), from Latin relevare "to raise, alleviate," from re-, intensive prefix, + levare "to lift up, lighten," from levis "not heavy" (see lever). The notion is "to raise (someone) out of trouble." Related: relieved; relieving.
reliever (n.): late 15c., agent noun from relieve. Baseball sense ("relief pitcher") is attested by 1945.
religieuse (n.): "a nun," 1690s, from French, fem. of religieux "monk," prop. "religious," from Old French religion (see religion). As a type of pastry, attested from 1929.
religion (n.): c.1200, "state of life bound by monastic vows," also "conduct indicating a belief in a divine power," from Anglo-French religiun (11c.), Old French religion "religious community," from Latin religionem (nominative religio) "respect for what is sacred, reverence for the gods," in Late Latin "monastic life" (5c.).

According to Cicero derived from relegere "go through again, read again," from re- "again" + legere "read" (see lecture (n.)). However, popular etymology among the later ancients (and many modern writers) connects it with religare "to bind fast" (see rely), via notion of "place an obligation on," or "bond between humans and gods." In that case, the re- would be intensive. Another possible origin is religiens "careful," opposite of negligens.

To hold, therefore, that there is no difference in matters of religion between forms that are unlike each other, and even contrary to each other, most clearly leads in the end to the rejection of all religion in both theory and practice. And this is the same thing as atheism, however it may differ from it in name. [Pope Leo XIII, Immortale Dei, 1885]
Meaning "particular system of faith" is recorded from c.1300. Modern sense of "recognition of, obedience to, and worship of a higher, unseen power" is from 1530s.
religiosity (n.): late 14c., from Late Latin religiositas, from religiosus (see religious).
religious (adj.): early 13c., from Anglo-French religius, Old French religious (12c., Modern French religieux) or directly from Latin religiosus, from religio (see religion). Transferred sense of "scrupulous, exact" is recorded from 1590s.
religiously (adv.): late 14c.; see religious + -ly (2). Transferred sense of "strictly, scrupulously" attested by 1570s.
relinquish (v.): late 15c., from Middle French relinquiss-, present participle stem of relinquir (12c.), from Latin relinquere "leave behind, forsake, abandon, give up," from re- "back" + linquere "to leave," from PIE *linkw-, from root *leikw- "to leave behind" (cf. Sanskrit reknas "inheritance, wealth," rinakti "leaves;" Greek leipein "to leave;" Gothic leihvan, Old English lænan "to lend;" Old High German lihan "to borrow;" Old Norse lan "loan"). Related: Relinquished; relinquishing.
reliquary (n.): "receptacle for keeping relics," 1650s, from French reliquaire (14c.), from Old French relique (see relic).
relique (n.): Frenchified spelling of relic (q.v.).
reliquiae (n.): "remains," 1650s, Latin, plural of reliquus "remaining," related to relinquere (perf. reliqui) "to leave behind" (see relinquish).
relish (v.): 1560s (implied in relished), from relish (n.). The sense of "to enjoy, take pleasure in" is from 1590s. Related: Relishing.
relish (n.): 1520s, "taste, flavor," alteration of reles "scent, taste, aftertaste," (early 14c.), from Old French relais, reles, "something remaining, that which is left behind," from relaisser (see release). Meaning "enjoyment of the taste or flavor of something" is attested from 1640s. Sense of "condiment" is first recorded 1797.
relive (v.): 1540s, "to come to life again" (also "to restore to life again"), from re- "back, again" + live (v.). Meaning "to experience over again" is attested from c.1711. Related: Relived; reliving.
reload (v.): 1778, from re- "back, again" + load (v.). Related: Reloaded; reloading.
relocate (v.): "to move to another place," 1834, from re- "back, again" + locate (v.). Related: Relocated; relocating.