Online Etymology Dictionary

runoff (n.): also run-off, "precipitation water drained by streams and rivers," 1887, from run (v.) + off (adv.). Meaning "deciding race after a tie" is from 1873; electoral sense is attested by 1910, American English.
runt (n.): c. 1500, "old or decayed tree stump," of unknown origin. Meaning extended to "small ox or cow" (1540s) and by 1610s generally to undersized animals and people. Specific American English sense of "smallest of a litter" (especially of pigs) is attested from 1841. Some see a connection to Middle Dutch runt "ox," but OED thinks this unlikely, and pronounces the word "of obscure origin." Related: Runty (1807).
runway (n.): "customary track of an animal," especially a deer, 1833, American English, from run (v.) + way (n.). Meaning "artificial sloping track" is attested from 1883; airfield sense is from 1923.
rupee (n.): Indian coin, 1610s, from Hindi or Urdu rupiyah, from Sanskrit rupyah "wrought silver," perhaps originally "something provided with an image, a coin," from rupah "shape, likeness, image."
Rupert: masc. proper name, probably a blend of German Ruprecht and English Robert.
rupture (n.): late 14c., originally medical, from Latin ruptura "the breaking (of an arm or leg), fracture," from past participle stem of rumpere "to break," from PIE *reup- "to snatch" (see rip (v.)). Specifically as "abdominal hernia" from early 15c.
rupture (v.): 1739, from rupture (n.). Related: Ruptured; rupturing. Ruptured duck (1945) was U.S. GI's dismissive term (based on its design) for the discharge button they were awarded.
rural (adj.): early 15c., from Old French rural (14c.), from Latin ruralis "of the countryside," from rus (genitive ruris) "open land, country," from PIE *reue- (1) "to open; space" (see room (n.)).
In early examples, there is usually little or no difference between the meanings of rural and rustic, but in later use the tendency is to employ rural when the idea of locality (country scenes, etc.) is prominent, and rustic when there is a suggestion of the more primitive qualities or manners naturally attaching to country life. [OED]
Related: Rurally.
rurban (adj.): 1918, a blend of rural and urban coined in reference to areas that have elements of both.
Ruritanian (adj.): "utopian," 1896, from Ruritania, name of an imaginary kingdom in "The Prisoner of Zenda" (1894) by Anthony Hope (1863-1933), who coined it from Latin rus (genitive ruris) "country" (see rural) + Latinate ending -itania (compare Mauritania).
ruse (n.): early 15c., "dodging movements of a hunted animal;" 1620s, "a trick," from Old French ruse, reuse "diversion, switch in flight; trick, jest" (14c.), back-formed noun from reuser "to dodge, repel, retreat; deceive, cheat," from Latin recusare "deny, reject, oppose," from re-, intensive prefix (see re-), + causari "plead as a reason, object, allege," from causa "reason, cause" (see cause (n.)). It also has been proposed that the French word may be from Latin rursus "backwards," or a Vulgar Latin form of refusare. Johnson calls it, "A French word neither elegant nor necessary." The verb ruse was used in Middle English.
rush (v.): mid-14c. (implied in rushing), "to drive back or down," from Anglo-French russher, from Old French ruser "to dodge, repel" (see ruse). Meaning "to do something quickly" is from 1650s; transitive sense of "to hurry up (someone or something)" is from 1850. U.S. Football sense originally was in rugby (1857).

Fraternity/sorority sense is from 1896 (originally it was what the fraternity did to the student); from 1899 as a noun in this sense. Earlier it was a name on U.S. campuses for various tests of strength or athletic skill between freshmen and sophomores as classes (1860).
rush (n.1): "plant growing in marshy ground," Old English resc, earlier risc, from Proto-Germanic *rusk- (source also of Middle Low German rusch, Middle High German rusch, German Rausch, West Frisian risk, Dutch rusch), from PIE *rezg- "to plait, weave, wind" (source also of Latin restis "cord, rope").

Old French rusche probably is from a Germanic source. Used for making torches and finger rings, also strewn on floors when visitors arrived; it was attested a type of "something of no value" from c. 1300. See OED for spelling variations.
rush (n.2): "a hasty driving forward," late 14c., from rush (v.). Sense of "mass migration of people" (especially to a gold field) is from 1848, American English. Football/rugby sense from 1857. Meaning "surge of pleasure" is from 1960s. Rush hour first recorded 1888. Rush order from 1896.
rusk (n.): "light, crisp bits of bread or biscuit," 1590s, from Spanish or Portuguese rosca "roll, twist of bread," literally "coil, anything round and spiral," of unknown origin, perhaps from a pre-Latin Iberian word.
Russell: masc. proper name, from Old French rous-el, diminutive of rous "red," used as a personal name. See russet.
russet (n.): mid-13c., "cloth of reddish-brown color," also (early 15c.) the color of this, from Old French rousset, from rosset (adj.) "reddish," diminutive of ros, rous "red," from Latin russus, which is related to ruber "red," from PIE *reudh- "red" (see red (adj.1)). As an adjective from late 14c. The word was applied to a type of apples first in 1620s, to a type of pears 1725.
Russia: 1530s, from Medieval Latin Russi "the people of Russia," from Rus, the native name of the people and the country (source of Arabic Rus, Medieval Greek Rhos), originally the name of a group of Swedish merchant/warriors who established themselves around Kiev 9c. and founded the original Russian principality; perhaps from Ruotsi, the Finnish name for "Sweden," from Old Norse Roþrslandi, "the land of rowing," old name of Roslagen, where the Finns first encountered the Swedes. This is from Old Norse roðr "steering oar," from Proto-Germanic *rothra- "rudder," from PIE *rot-ro-, from root *ere- (1) "to row" (see row (v.)).

Derivation from the IE root for "red," in reference to hair color, is considered less likely. Russian city-states were founded and ruled by Vikings and their descendants. The Russian form of the name, Rossiya, appears to be from Byzantine Greek Rhosia. Russification is from 1842.
Russian (n.): 1530s, from Medieval Latin Russianus, from Russia (see Russia). Slang or colloquial Russki "Russian" (1858) is from Russian Russkiy. Russian roulette attested from 1937. Russian dressing for salads is from 1915.
Russo-: word-forming element meaning "pertaining to Russia, Russians, or the Russian language," from comb. form of Medieval Latin Russi (plural) "the Russians" (see Russia).
rust (n.): "red oxide of iron," Old English rust "rust; moral canker," related to rudu "redness," from Proto-Germanic *rusta- (source also of Frisian rust, Old High German and German rost, Middle Dutch ro(e)st), from PIE *reudh-s-to- (source also of Lithuanian rustas "brownish," rudeti "to rust;" Latin robigo, Old Church Slavonic ruzda "rust"), from root *reudh- "red" (see red (adj.1)).

As a plant disease, attested from mid-14c. Rust Belt "decayed urban industrial areas of mid-central U.S." (1984) was popularized, if not coined, by Walter Mondale's presidential campaign.
rust (v.): early 13c., from rust (n.). Transitive sense "cause to rust" is from 1590s. Related: Rusted; rusting.
rustic (adj.): mid-15c., from Latin rusticus "of the country, rural; country-like, plain, simple, rough, coarse, awkward," from rus (genitive ruris) "open land, country" (see rural). Noun meaning "a country person, peasant" is from 1550s (also in classical Latin). Related: Rustical (early 15c.).
rusticate (v.): 1650s, from Latin rusticatus, past participle of rusticarti "to live in the country" (see rustication). Related: Rusticated; rusticating.
rustication (n.): 1620s, "to reside in the country," back-formation from rustication, or else from Latin rusticationem (nominative rusticatio) "act or fact of living in the country," noun of action from past participle stem of rusticari "live or stay in the country," from rusticus (see rustic). Meaning "send into the country" is from 1714.
rusticity (n.): 1530s, from Middle French rusticite (15c.), from Latin rusticitatem (nominative rusticitas) "country life," from rusticus (see rustic (adj.)).
rustle (v.): "to emit soft, rapid sounds," late 14c. (implied in rustling), of uncertain origin, perhaps imitative (compare Middle Low German ruschen, Middle Dutch ruusscen, German rauschen "to rustle"). Related: Rustled; rustling. Meaning "steal" (especially cattle) first attested 1882, probably from earlier American English slang sense of "move about vigorously" (1844), perhaps a separate word, compounded from rush and hustle.
rustle (n.): 1759, from rustle (v.).
rustler (n.): 1820, "one who rustles," agent noun from rustle (v.). American English meaning "cattle thief" is from 1882.
rusty (adj.): Old English rustig; see rust (n.) + -y (2). Cognate with Frisian roastich, Middle Dutch roestich, Dutch roestig, Old High German rostag, German rostig. "In the 16th and 17th centuries frequently used as a term of general disparagement" [OED]. Of bodily skills, "impaired by neglect," from c. 1500; of mental qualities, accomplishments, etc., first attested 1796.
rut (n.1): "narrow track worn or cut in the ground," 1570s, probably from Middle English route (see route (n.)); though OED finds this "improbable." Metaphoric meaning "narrow, monotonous routine; habitual mode of behavior" first attested 1839.
rut (n.2): "annually recurring sexual excitement in animals; animal mating season" (originally of deer), early 15c., from Old French rut, ruit, from Late Latin rutigum (nominative rugitus) "a bellowing," from past participle of Latin rugire "to bellow," from PIE imitative root *reu-. The verb is recorded from early 15c. Related: Rutting.
rutabaga (n.): 1799, from Swedish dialectal (West Götland) rotabagge, from rot "root" (see root (n.)) + bagge "bag" (see bag (n.)). Slang meaning "dollar" is from 1940s.
Ruth: fem. proper name, biblical ancestor of David, from Hebrew Ruth, probably a contraction of reuth "companion, friend, fellow woman."
ruth (n.): "sorrow for the misery of another; repentance, regret," c. 1200, ruthe, from Old Norse hryggð "ruth, sorrow," from hryggr "sorrowful, grieved" (see rue (v.)) + Proto-Germanic abstract noun suffix *-itho (see -th (2)). Or else formed in English from reuwen "to rue" on the model of true/truth, etc. The Old English word was rue (n.2).
Ruthenian (adj.): 1850, of or pertaining to the Ukrainian people (earlier Ruthene, 1540s), from Medieval Latin Rutheni "the Little Russians," a derivative of Russi (see Russia). For consonant change, compare Medieval Latin Prut(h)eni, from Prussi "Prussians." Another word in the same sense was Russniak.
ruthenium (n.): metallic element, 1845, named by Russian chemist Karl Klauss, from a name proposed earlier (1828) in reference to a metal extracted from ores from the Ural Mountains of Russia (see Ruthenian). With metallic element ending -ium.
ruthless (adj.): early 14c., from reuthe "pity, compassion" (see ruth) + -less. Ruthful (early 13c.) has fallen from use since late 17c. except as a deliberate archaism. Related: Ruthlessly; ruthlessness.
Ruy Lopez (n.): type of chess opening, 1876, from Ruy López de Segura (fl. 1560), Spanish bishop and writer on chess, who developed it.
RV (n.): short for recreational vehicle, by 1967.
Rwanda: African nation, named for indigenous people there, whose word for themselves is of unknown origin.
rye (n.): Old English ryge, from Proto-Germanic *ruig (source also of Old Saxon roggo, Old Norse rugr, Old Frisian rogga, Middle Dutch rogghe, Old High German rocko, German Roggen), related to or from Balto-Slavic words (such as Old Church Slavonic ruži, Russian rozh' "rye;" Lithuanian rugys "grain of rye," plural rugiai), from a European PIE root *wrughyo- "rye." Meaning "whiskey" (made from rye) first attested 1835. Rye bread attested from mid-15c.