Online Etymology Dictionary

roundhouse (n.): 1580s, from Dutch rondhuis "guardhouse."
roundtable (n.): in reference to a gathering of persons in which all are accorded equal status, 1826 (there being no head of a round table.) King Arthur's Round Table is attested from c.1300, from Old French table ronde (1155, in Wace's Roman de Brut).
roundup (n.): by 1869 in the cattle drive sense; from verbal phrase round up "to collect in a mass" (1610s; specifically of livestock from 1847); see round (v.) + up. Meaning "summary of news items" is recorded from 1886.
rouse (v.): mid-15c., probably from Anglo-French, or Old French, originally used of hawks shaking the feathers of the body, but like many hawking terms of obscure origin. Meaning "to stir up, provoke to activity" is from 1580s; that of "awaken" is first recorded c.1590. Related: Roused; rousing.
roust (v.): 1650s, probably an alteration of rouse.
roustabout (n.): "deck hand, wharf worker," 1868, perhaps from roust + about. But another theory connects it to British dialect rousing "rough, shaggy," a word associated perhaps with rooster.
rout (n.): 1590s, "disorderly retreat," from Middle French route "disorderly flight of troops," literally "a breaking off, rupture," from Vulgar Latin rupta "a dispersed group," literally "a broken group," from Latin rupta, fem. past participle of rumpere "to break" (see rupture (n.)).
rout (v.): c.1600, from rout (n.). Related: Routed; routing.
route (n.): early 13c., from Old French rute "road, way, path," from Latin rupta (via) "(a road) opened by force," from rupta, fem. past participle of rumpere "to break" (see rupture). Sense of "fixed or regular course for carrying things" (cf. mail route) is 1792, an extension of the meaning "customary path of animals" (early 15c.).
router (n.): "cutter that removes wood from a groove," 1818, from rout "poke about, rummage" (1540s), originally of swine digging with the snout; a variant of root (v.1).
routine (n.): 1670s, from French routine "usual course of action, beaten path" from route "way, path, course" (see route) + subst. suffix -ine. Theatrical sense is from 1926. The adjective is attested from 1817, from the noun.
routinization (n.): 1916, noun of action from routinize (1893), from routine + -ize.
roux (n.): 1813, from French roux "red, browned," from Latin russus (see russet).
rove (v.): "to wander with no fixed destination," 1530s, possibly a Midlands dialectal variant of northern English and Scottish rave "to wander, stray," from Middle English raven, probably from Old Norse rafa "to wander, rove." Influenced by rover. Earliest sense was "to shoot arrows at a mark selected at pleasure or at random" (late 15c.). Related: Roved; roving.
rover (n.): late 14c., "sea-robber, pirate," from Middle Dutch rover "robber, predator, plunderer," especially in zeerovere "pirate," literally "sea-robber," from roven "to rob," from Middle Dutch root "spoil, plunder," related to Old English reaf "spoil, plunder," reafian "to reave" (see reft).
row (n.1): "line of people or things," Old English ræw "a row, line," from Proto-Germanic *rai(h)waz (cf. Middle Dutch rie, Dutch rij "row;" Old High German rihan "to thread," riga "line;" German Reihe "row, line, series;" Old Norse rega "string"), possibly from PIE root *rei- "to scratch, tear, cut" (cf. Sanskrit rikhati "scratches," rekha "line"). Meaning "a number of houses in a line" is attested from mid-15c., originally chiefly Scottish and northern English. Phrase a hard row to hoe attested from 1823, American English.
row (v.): "propel with oars," Old English rowan (class VII strong verb; past tense reow, past participle rowen), from Proto-Germanic *ro- (cf. Old Norse roa, Dutch roeien, West Frisian roeije, Middle High German rüejen), from PIE root *ere- (1) "to row" (cf. Sanskrit aritrah "oar;" Greek eressein "to row," eretmon "oar," trieres "trireme;" Latin remus "oar;" Lithuanian iriu "to row," irklas "oar;" Old Irish rome "oar," Old English roðor "rudder").
row (n.2): "noisy commotion," 1746, Cambridge University slang, of uncertain origin, perhaps related to rousel "drinking bout" (c.1600), a shortened form of carousal. Klein suggests a back-formation from rouse (n.), mistaken as a plural (cf. pea from pease).
row-house (n.): 1913, American English, from row (n.1), which is attested from mid-15c. in sense of "a number of houses in a line," + house (n.).
rowan (n.): "mountain ash," 1804, from rowan-tree, rountree (1540s), northern English and Scottish, from a Scandinavian source (cf. Old Norse reynir, Swedish Ronn "the rowan"), ultimately from the root of red, in reference to the berries.
There were those in this neighbourhood, long after the beginning of the present century, who believed that a slip of rowan tree carried on their person dispelled glamour, and rendered nugatory all the powers of sorcery and witchcraft. [Alexander Laing, "Lindores Abbey and the Burgh of Newburgh," Edinburgh, 1876]
rowboat (n.): 1530s, from row (v.) + boat. Cf. Dutch roeiboot.
rowdy (n.): "a rough, quarrelsome person," 1808, American English, originally "lawless backwoodsman," probably from row (n.2). The adjective is first recorded 1819. Related: Rowdily; rowdiness.
rowel (n.): "pointed wheel on a spur," mid-14c., from Old French roelle "small wheel" (see roulette).
Roxanne: fem. proper name, from French, from Latin Roxane, from Greek Rhoxane, of Persian origin (cf. Avestan raoxšna- "shining, bright").
Roxy: cinema chain built by U.S. entertainment mogul Samuel Latin "Roxy" Rothafel (1882-1936).
royal (adj.): mid-13c., from Old French roial, from Latin regalis, from rex (genitive regis) "king" (see rex). Battle royal (1670s) preserves the French custom of putting the adjective after the noun (cf. attorney general); the sense of the adjective here is "on a grand scale" (cf. pair-royal "three of a kind in cards or dice," c.1600). As a modifier meaning "thorough, total" royal is attested in English from 1940s. The Royal Oak was a tree in Boscobel in Shropshire in which Charles II hid himself during flight after the Battle of Worcester in 1651. Sprigs of oak were worn to commemorate his restoration in 1660.
royale (adj.): French, literally "royal" (see royal).
royalist (n.): 1640s, from royal + -ist.
royalty (n.): late 14c., "office or position of a sovereign," from Old French roialte, from Vulgar Latin *regalitatem (nominative *regalitas), from Latin regalis (see royal). Sense of "prerogatives or rights granted by a sovereign to an individual or corporation" is from late 15c. From that evolved more general senses, such as "payment to a landowner for use of a mine" (1839), and ultimately "payment to an author, composer, etc." for sale or use of his or her work (1857).
rpg (n.): by 1979, initialism from role-playing game. As an initialism for rocket-propelled grenade, by 1970.
rpm: 1906, initialism from revolutions per minute.
rRNA (n.): stands for ribosomal RNA.
rub (v.): late 14c., perhaps related to East Frisian rubben "to scratch, rub," and Low German rubbeling "rough, uneven," or similar words in Scandinavian (cf. Danish rubbe "to rub, scrub," Norwegian rubba), of uncertain origin. Related: Rubbed; rubbing.

Hamlet's there's the rub (1602) preserves a noun sense of "obstacle, inequality on ground" first recorded 1580s and common in 17c. To rub (someone) the wrong way is from 1853, probably the notion is of cats. To rub noses in greeting as a sign of friendship (attested from 1822) formerly was common among Eskimos, Maoris, and some other Pacific Islanders. Rub out "obliterate" is from 1560s; underworld slang sense of "kill" is recorded from 1848, American English. Rub off "have an influence on" is recorded from 1959.
rub-a-dub: 1787, echoic of the sound of a drum.
rubaiyat (n.): "quatrains" (in Persian poetry), 1859, plural of rubai, from Arabic rubaiyah, from rubaiy "composed of four elements."
rubato: 1883, short for tempo rubato, literally "robbed time."
rubber (n.): "thing that rubs," 1530s, agent noun from rub (v.). The meaning "elastic substance from tropical plants" (short for India rubber) first recorded 1788, introduced to Europe 1744 by Charles Marie de la Condamine, so called because it was originally used as an eraser.
Very useful for erasing the strokes of black lead pencils, and is popularly called rubber, and lead-eater. [entry for Caoutchouc in Howard, "New Royal Encyclopedia," 1788]
Meaning "overshoes made of rubber" is 1842, American English; slang sense of "condom" is from 1930s. Sense of "deciding match" in a game or contest is 1590s, of unknown signification, and perhaps an entirely separate word. Rubber stamp is from 1881; figurative sense of "institution whose power is formal but not real" is from 1919; the verb in this sense is from 1934. Rubber cement is attested from 1856 (from 1823 as India-rubber cement). Rubber check (one that "bounces") is from 1927.
rubberneck (n.): 1897, "person who is always listening to other people's conversation; person who gazes around him with undue curiosity," from rubber + neck (n.). Popularized with reference to sightseers in automobiles. Also as a verb from 1897. Related: Rubbernecking; rubbernecker.
rubbish (n.): c.1400, from Anglo-French rubouses (late 14c.), of unknown origin. Apparently somehow related to rubble. The verb sense of "disparage, criticize harshly" is first attested 1953 in Australian and New Zealand slang.
rubble (n.): c.1400, from Anglo-Norm. *robel "bits of broken stone," probably related to rubbish, but also possibly from Old French robe (see rob).
rube (n.): 1896, reub, from shortened form of masc. proper name Reuben (q.v.), which is attested from 1804 as a conventional type of name for a country man.
Rube Goldberg: 1940, from the U.S. cartoonist Reuben Lucius Goldberg (1883-1970) who devised fantastically complex gadgetry to accomplish simple tasks. His British counterpart was Heath Robinson (1872-1944).
rubella (n.): "German measles," 1883, Modern Latin, literally "rash," from neuter plural of Latin rubellus "reddish," diminutive of ruber "red" (see red).
Rubenesque (adj.): of a woman's body, "rounded and alluringly plump," 1904, of the type characteristic of the paintings of Flemish painter Sir Peter Paul Rubens (1577-1640).
Rubicon (n.): in phrase "to cross (or "pass") the Rubicon "take a decisive step," 1620s, a reference to a small stream to the Adriatic on the coast of northern Italy, which in ancient times formed part of the southern boundary of Cisalpine Gaul; crossed by Caesar Jan. 10, 49 B.C.E., when he left his province to attack Pompey. The name is from Latin rubicundus "ruddy," in reference to the color of the soil on its banks.
rubicund (adj.): c.1500, from French rubicond or directly from Latin rubicundus, from rubere "to be red," from ruber "red" (see red). Related: Rubicundity.
Rubik's Cube (n.): 1980, named for teacher Ernö Rubik (b.1944) who patented it in Hungary in 1975.
ruble (n.): unit of Russian monetary system, 1550s, via French, from Russian rubl', perhaps from rubiti "to chop, cut," so called because the original metallic currency of Russia (14c.) consisted of silver bars, from which the necessary amount was cut off.
rubric (n.): late 14c., "directions in religious services" (often in red writing), from Old French rubrique, from Latin rubrica "red ochre, red coloring matter," from ruber, from PIE root *rudhro- (see red).
ruby (n.): c.1300, from Old French rubi (12c.), from Medieval Latin rubinus lapis "red stone" (cf. Italian rubino), from Latin rubeus "red," related to ruber (see red). Modern French rubis is not eexplained; Klein suggests a plural mistaken for singular.