Online Etymology Dictionary

ruche (n.): 1827, from French ruche, literally "beehive" (13c.), of Celtic origin (cf. Breton rusken), from Proto-Celtic *rusca "bark." Related: Ruched; ruching.
rucksack (n.): 1866, from German Rucksack, from Alpine dialect Rück "the back" (from German Rücken) + Sack "sack."
ruckus (n.): 1890, possibly a blend of ruction and rumpus.
ruction (n.): "disturbance," 1825, dialectal or colloquial, of unknown origin.
rudder (n.): Old English roðor "paddle, oar," from Proto-Germanic *rothru- (cf. Old Frisian roder, Middle Low German roder, Middle Dutch roeder, Dutch roer, Old High German ruodar, German Ruder "oar"), from *ro- "steer" (see row (v.)) + suffix -þra, used to form neutral names of tools. Meaning "broad, flat piece of wood attached to the stern of a boat and used for steering" is from c.1300. Spelling with -d- for -th- first recorded mid-15c.
ruddy (adj.): Old English rudig, probably from rudu "redness," related to read "red" (see red). As a British slang euphemism for bloody (q.v.), first recorded 1914.
rude (adj.): late 13c., "coarse, rough" (of surfaces), from Latin rudis "rough, crude, unlearned," perhaps related to rudus "rubble." Sense of "ill-mannered" is from late 14c. Rude boy (also rudie, for short) in Jamaican slang is attested from 1967. Figurative phrase rude awakening is attested from 1895.
Rudesby (n.): "insolent person," 1560s, mock surname from rude.
rudiment (n.): 1540s, from Middle French rudiment (16c.), from Latin rudimentum "early training, first experience, beginning, first principle," from rudis "unlearned, untrained" (see rude).
rudimentary (adj.): 1827; see rudiment + -ary.
Rudolph: masc. proper name, from German Rudolf, from Old High German Hrodulf, literally "fame-wolf," from hruod- "fame, glory" + wolf.
Rudra: storm god in Vedic mythology, from Sanskrit Rudrah, literally "the howler, roarer," from stem of rudati "weeps, laments, bewails," cognate with Latin rudere "to roar, bellow," Lithuanian rauda "wail, lamentation," Old English reotan "to wail, lament."
rue (v.): "feel regret," Old English hreowan "make sorry, distress, grieve" (class II strong verb; past tense hreaw, past participle hrowen), from Proto-Germanic *khrewanan (cf. Old Frisian riowa, Middle Dutch rouwen, Old Dutch hrewan, German reuen); in part, blended with Old English weak verb hreowian "feel pain or sorrow," and perhaps influenced by Old Norse hryggja "make sad," both from Proto-Germanic *khruwjanan, from the same root; from PIE root *kreue- (2) "to push, strike" (see anacrusis). Related: Rued; ruing.
rue (n.1): "perennial evergreen shrub," late 14c., from Old French rue, earlier rude, from Latin ruta "rue," probably from Greek rhyte, of uncertain etymology, originally a Peloponnesian word. The bitter taste of its leaves led to many punning allusions to the noun form of rue (v.).
rue (n.2): "sorrow, repentance," Old English hreow, from rue (v.).
rue (n.3): French for "street," from Vulgar Latin *ruga (cf. Old Italian ruga), properly "a furrow," then in Medieval Latin "a path, street."
rueful (adj.): early 13c., rewfulle, reowfule, from rue (v.) + -ful.
ruefully (adv.): early 13c., reufulike; see rueful + -ly (2).
ruff (n.): kind of large collar, stiffly starched, especially common in the seventeenth century," 1520s, originally in reference to sleeves (of collars, from 1550s), probably a shortened form of ruffle. Card-playing sense is a separate word, from a former game of that name (1580s), from Middle French roffle, earlier romfle (early 15c.), from Italian ronfa, perhaps a corruption of trionfo "triumph" (from French; cf. trump). The game was in vogue c.1590-1630.
ruffian (n.): 1530s, from Middle French rufian "a pimp," from Italian ruffiano "a pander, pimp," of uncertain origin, perhaps from a Germanic source related to rough (q.v.), but Dutch roffiaan, German Ruffian are said to be from French. English meaning might have been influenced by similarity of sound to rough. The Romanic words (e.g. Medieval Latin ruffianus, Provençal rufian, Catalan rufia, Spanish rufian) preserve the sense of "protector or owner of whores." For sense evolution in English, cf. bully (n.).
ruffle (v.): c.1300, "to disturb the smoothness of," perhaps from Old Norse hrufla "to scratch," or Low German ruffelen "to wrinkle, curl," both of unknown origin. Meaning "disarrange" (hair or feathers) first recorded late 15c.; sense of "annoy, distract" is from 1650s. Related: Ruffled; ruffling.
ruffle (n.): "ornamental frill," 1707, from ruffle (v.).
rufous (adj.): "reddish-brown," 1782, from Latin rufus "red, reddish, red-haired," from Osco-Umbrian cognate of Latin ruber "red" (see red).
Rufus: masc. proper name, literally "red-haired," from Latin rufus (see rufous).
rug (n.): 1550s, "coarse fabric," of Scandinavian origin, cf. Norwegian dialectal rugga "coarse coverlet," from Old Norse rogg "shaggy tuft," perhaps related to rag and perhaps also rough. Sense evolved to "coverlet, wrap" (1590s), then "mat for the floor" (1808). Meaning "toupee" is theater slang from 1940. Cut a rug "dance" is slang first attested 1942. To sweep (something) under the rug in the figurative sense is from 1954.
rugae (n.): plural of ruga (1775), from Latin ruga "a wrinkle in the face."
rugby (n.): 1864, after Rugby, public school where the game was played, from city of Rugby in Warwickshire, central England. The place name is Rocheberie (1086) "fortified place of a man called *Hroca;" with second element from Old English burh (dative byrig), replaced by 13c. with Old Norse -by "village" due to the influence of Danish settlers. Otherwise it might be *Rockbury today. First element perhaps rather Old English hroc "rook." Rugby Union formed 1871. Slang rugger for "rugby player" is from 1893.
rugged (adj.): early 14c., "rough, shaggy, careworn" (originally of animals), from Old Norse rogg "shaggy tuft" (see rug). "The precise relationship to ragged is not quite clear, but the stem is no doubt ultimately the same" [OED]. Meaning "strong, robust" is American English, 1848.
We were challenged with a peace-time choice between the American system of rugged individualism and a European philosophy of diametrically opposed doctrines -- doctrines of paternalism and state socialism. [Herbert Hoover, 1928]
rugrat (n.): also rug-rat, "baby, child," by 1968; see rug + rat (n.).
ruin (n.): late 14c., "act of giving way and falling down," from Old French ruine, from Latin ruina "a collapse" (cf. Spanish ruina, Italian rovina), related to ruere "to rush, fall violently, collapse," of unknown origin. Meaning "complete destruction of anything" is from 1670s. Ruins "remains of a decayed building or town" is from mid-15c.
ruin (v.): 1580s, from ruin (n.). Financial sense is attested from 1660. Related: Ruined; ruining.
ruination (n.): 1660s, from verb ruinate (1540s), from Medieval Latin ruinatus, past participle of ruinare, from Latin ruina (see ruin).
ruinous (adj.): late 14c., from French ruineux or directly from Latin ruinosus, from ruina (see ruin). Related: Ruinously.
rule (n.): early 13c., "principle or maxim governing conduct," from Old French riule, from Vulgar Latin *regula, from Latin regula "straight stick, bar, ruler, pattern," related to regere "to rule, straighten, guide" (see regal). Replaced Old English wealdan. Meaning "regulation governing play of a game, etc." is from 1690s. Phrase rule of thumb first attested 1690s. Rule of law "supremacy of impartial and well-defined laws to any individual's power" is from 1883. Meaning "Strip used for making straight lines" is recorded from mid-14c. Typography sense is attested from 1680s.
rule (v.): early 13c., "to control, guide, direct," from Old French riuler, from Latin regulare (see regulate). Legal sense is recorded from early 15c. "Rule Brittania," patriotic song, is from 1740. Related: Ruled; ruling.
ruler (n.): "one who rules," late 14c., agent noun from rule (v.). Meaning "strip used for making straight lines" is c.1400 (see rule (n.)).
ruling (n.): "judicial decision," 1550s, verbal noun from rule (v.).
rum (n.): "liquor from sugar cane or molasses," 1650s, originally rumbullion (1651), rombostion (1652), of uncertain origin, perhaps from rum (adj.).
The chiefe fudling they make in the Island [i.e. Barbados] is Rumbullion alias Kill-Devill, and this is made of suggar cane distilled, a hott, hellish and terrible liquor. [1651]
The English word was borrowed into Dutch, German, Swedish, Danish, Spanish, Portuguese, Italian, French, and Russian. Used since 1800 in North America as a general (hostile) name for intoxicating liquors. Rum-runner "smuggler or transporter of illicit liquor" is from 1919.
rum (adj.): "excellent," 1560s, from rome "fine" (1560s), said to be from Romany rom "male, husband" (see Romany). A very common 16c. cant word, by 1774 it had come to mean "odd, strange, bad, spurious," perhaps because it had been so often used approvingly by rogues in reference to one another. This was the main sense after c.1800.
rumba (n.): 1919, from Cuban Spanish rumba, originally "spree, carousal," derived from Spanish rumbo "spree, party," earlier "ostentation, pomp, leadership," perhaps originally "the course of a ship," from rombo "rhombus," in reference to the compass, which is marked with a rhombus. The verb is recorded from 1944.
rumble (v.): late 14c., probably related to Middle Dutch rommelen "to rumble," Middle High German rummeln, Old Norse rymja "to shout, roar," all of imitative origin. The noun is attested from late 14c. Slang noun meaning "gang fight" is from 1946. Meaning "backmost part of a carriage" is from 1808 (earlier rumbler, 1801), probably from the effect of sitting over the wheels; hence rumble seat (1828). Related: Rumbled; rumbling.
rumbustious (adj.): 1778, an arbitrary formation (perhaps suggested by rum (adj.) and boisterous, robustious, bumptious, etc.) from robustious.
rumen (n.): 1728, from Latin rumen "the throat."
ruminant (n.): 1660s, from Latin ruminantem (nominative ruminans), present participle of ruminare "to chew the cud" (see ruminate).
ruminate (v.): 1530s, "to turn over in the mind," also "to chew cud" (1540s), from Latin ruminatus, past participle of ruminare "to chew the cud, turn over in the mind," from rumen (genitive ruminis) "gullet," of uncertain origin. Related: Ruminated; ruminating.
rummage (v.): 1520s, "act of arranging cargo in a ship," a shortening of Middle French arrumage "arrangement of cargo," from arrumer "to stow goods in the hold of a ship," from a- "to" + rumer, probably from Germanic (cf. Old Norse rum "compartment in a ship," Old High German rum "space," Old English rum, see room). Meaning "to search (the hold of a ship) thoroughly" first recorded 1620s. Related: Rummaged; rummaging. Rummage sale (1803) originally was a sale at docks of unclaimed goods.
rummy (n.): card game, 1910, rhummy, of unknown origin. Gin rummy is first attested 1941. Meaning "drunkard" is 1851, from rum (n.). Meaning "opponent of temperance" in U.S. politics is from 1860.
rumor (n.): late 14c., from Old French rumour "widespread noise or report" (French rumeur), from Latin rumorem (nominative rumor) "noise, clamor, common talk, rumor," related to ravus "hoarse." Rumor mill is from 1887.
rumor (v.): 1610s (implied in rumored), "spread a rumor," from rumor (n.). Related: Rumoring.
rump (n.): "hind-quarters, buttocks of an animal," mid-15c., from a Scandinavian source (cf. Danish, Norwegian rumpe, Swedish rumpa), cognate with Middle Dutch romp, German Rumpf "trunk, torso." Sense of "small remnant" derives from "tail" and is first recorded 1640s in reference to the English Rump Parliament (December 1648-April 1653).