Online Etymology Dictionary

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.
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.