Online Etymology Dictionary

Rio de Janeiro: literally "January River," named by explorer Amerigo Vespucci because he discovered it on Jan. 1, 1502, and so called because he incorrectly thought the bay was the estuary of a large river. See January.
riot (n.): early 13c., "debauchery, extravagance, wanton living," from Old French riote (masc. riot) "dispute, quarrel," perhaps from Provençal riota, of uncertain origin. Meaning "public disturbance" is first recorded late 14c. Meaning "something spectacularly successful" first recorded 1909 in theater slang. Run riot is first recorded 1520s, a metaphoric extension from Middle English meaning in reference to hounds following the wrong scent. The Riot Act, part of which must be read to a mob before active measures can be taken, was passed 1714 (1 Geo. I, st.2, c.5). Riot girl and alternative form riot grrl first recorded 1992.
riot (v.): late 14c., "behave in a dissolute manner, engage in loose revelry," from Old French riotter, from riote (see riot (n.)). Related: Rioted; rioting.
riotous (adj.): late 14c., from Old French riotous, from riote (see riot). Related: Riotously; riotousness.
rip (v.): "tear apart," late 15c., probably of North Sea Germanic origin (cf. Flemish rippen "strip off roughly," Frisian rippe "to tear, rip") or else from a Scandinavian source (cf. Swedish reppa, Danish rippe "to tear, rip"). In either case, probably imitative of the sound of cloth ripping.

Meaning "to move with slashing force" (1798) is the sense in let her rip, American English colloquial phrase attested from 1853. The noun is attested from 1711; rip cord (1909) originally was in ballooning. The verbal phrase rip off "to steal or rob," is first recorded c.1967 in black slang, but rip was prison slang for "to steal" since 1904, and was also used in this sense in 12c. Rip-off (n.) is attested from 1970.
rip (n.1): "rough water," 1775, perhaps a special use of rip (v.). Originally of seas; application to rivers is from 1857. Rip-tide (also riptide) is attested from 1862 but isn't a tide.
rip (n.2): "thing of little value," 1815, earlier "inferior or worn-out horse" (1778), perhaps altered from slang rep (1747) "man of loose character," which is itself perhaps short for reprobate (q.v.).
Rip Van Winkle: "person out of touch with current conditions," 1829, from name of character in Washington Irving's "Sketch Book" (1819-20).
riparian (adj.): "of or pertaining to river banks," 1849, from Latin riparius "of a river bank," from riparia "shore," later used in reference to the stream flowing between the banks, from ripa "(steep) bank of a river, shore," probably literally "break" (and indicating the drop off from ground level to the stream bed), or else "that which is cut out by the river," from PIE root *rei- "to scratch, tear, cut" (cf. Greek ereipia "ruins," eripne "slope, precipice;" Old Norse rifa "break, to tear apart;" Danish rift "breach," Middle High German rif "riverbank, seashore;" cf. riven, rift, rifle).
ripe (adj.): Old English ripe "ready for reaping, fit for eating," from West Germanic *ripijaz (cf. Middle Dutch ripe, Dutch rijp, Old High German rifi, German reif); related to Old English repan "to reap" (see reap).
ripen (v.): "to grow ripe," 1560s, from ripe + -en (1). Related: Ripened; ripening. Earlier, the verb was simply ripe, from late Old English ripian, from the adjective.
riposte (n.): 1707, "a quick thrust after parrying a lunge," a fencing term, from French riposte, by dissimilation from risposte, from Italian risposta "a reply," from rispondere "to respond," from Latin respondere (see respond). Sense of "sharp retort" is first attested 1865.
ripper (n.): 1610s, agent noun from rip (v.). Meaning "killer who mutilates his victims" (1890) is from Jack the Ripper, notorious London murderer, whose nickname contains a pun on ripper in sense of "tool for ripping" old slates, etc. (1823) and the slang meaning "excellent person or thing, a 'ripping' fellow" (1838), from ripping "excellent, splendid" (1826).
ripple (v.): 1660s, "to present a ruffled surface," of unknown origin, perhaps a frequentative of rip (v.). Related: Rippled; rippling.
ripple (n.): "very small wave," 1798, from earlier meaning "stretch of shallow, rippling water" (1755), from ripple (v.). Meaning "ice cream streaked with colored syrup" first attested 1939, so called from its appearance.
riprap (n.): also rip-rap, "loose stone thrown down in water or soft ground as foundation," 1822, American English, from earlier nautical meaning "stretch of rippling water" (often caused by underwater elevations), 1660s, probably of imitative origin (cf. riprap "a sharp blow," 1570s).
riproaring (adj.): 1834, altered from riproarious (1830), from rip (v.) "tear apart" + (up)roarious (1819); see uproar.
ripsnorter (n.): "something of exceptional strength," 1840, probably from rip (v.) + snort (v.).
rise (v.): Old English risan (usually arisan; class I strong verb; past tense ras, past participle risen), from Proto-Germanic *us-risanan "to go up" (cf. Old Norse risa, Gothic urreisan "to rise," Old High German risan "to rise, flow," German reisen "to travel," originally "to rise for a journey"). Related to raise. The noun meaning "upward movement" is from 1570s; the meaning "a piece of rising ground" is from 1630s. Phrase to get a rise out of (someone) (1834) is a metaphor from angling (1650s).
riser (n.): late 14c., agent noun from rise (v.). Meaning "upright part of a step" is from 1771.
risible (adj.): 1550s, "given to laughter," from Late Latin risibilis "laughable, able to laugh," from Latin risus, past participle of ridere "to laugh." Meaning "capable of exciting laughter, comical" is from 1727.
risk (n.): 1660s, risque, from French risque, from Italian risco, riscio (modern rischio), from riscare "run into danger," of uncertain origin. The anglicized spelling first recorded 1728. Spanish riesgo and German Risiko are Italian loan-words. Risk aversion is recorded from 1942; risk factor from 1906; risk management from 1963; risk taker from 1892.
risk (v.): 1680s, from risk (n.). Related: Risked; risks; risking.
risky (adj.): 1826, from risk (n.) + -y (2).
risorgimento (n.): 1889, "movement which led to the unification and independence of Italy," Italian, literally "uprising" (of Italy against Austria, c.1850-60), from risorgere, from Latin resurgere (see resurgent).
risotto (n.): rice cooked in broth with meat and cheese, 1848, from Italian risotto, from riso "rice" (see rice). At first in Italian contexts; it begins to appear in English cookery books c.1880.
risque (adj.): "tending toward impropriety," 1867, borrowed from French risqué, past participle of risquer (see risk).
Ritalin: proprietary name (Ciba Ltd., originally in Switzerland) for drug methylphenidate hydrochloride, copyrighted 1948, years before the drug itself was marketed.
ritardando: 1811, from Italian, present participle of ritardare, from Latin retardare (see retardation).
rite (n.): early 14c., from Latin ritus "religious observance or ceremony, custom, usage," perhaps from PIE root *re(i)- "to count, number" (cf. Greek arithmos "number," Old English rim "number;" see read). Rite of passage (1909) is translated from French rite de passage, coined by French anthropologist Arnold van Gennep (1873-1957).
ritual (adj.): 1560s, from Latin ritualis "relating to (religious) rites," from ritus "rite" (see rite). The noun is first recorded 1640s.
ritualistic (adj.): 1844; see ritual + -istic.
ritz: "high quality, superiority," 1910 (Ritzian, adj., is attested by 1908), in reference to the luxurious Ritz hotels in N.Y., London, Paris, etc., commemorating Swiss hotelier César Ritz (1850-1918). To put on the ritz "assume an air of superiority" is recorded from 1926. A verb ritz "to behave haughtily" is recorded from 1911.
ritzy: 1920, from ritz + -y (2). Related: Ritziness.
rival (n.): 1570s, from Latin rivalis "a rival," originally, "one who uses the same stream" (or "one on the opposite side of the stream"), from rivus "brook" (see rivulet). The notion is of the competitiveness of neighbors.
rival (v.): c.1600, from rival (n.). Related: Rivaled; rivaling.
rivalry (n.): 1590s; from rival + -ery. Rivality in the same sense is recorded from 1580s.
rive (v.): "tear in pieces, strike asunder," late 13c., from Old Norse rifa "to tear apart" (see riparian).
riven (adj.): "split, cloven, rent," c.1300, past participle adjective from rive "to tear, rend."
river (n.): c.1300, from Old French riviere, from Vulgar Latin *riparia "riverbank, seashore, river" (cf. Spanish ribera, Italian riviera), noun use of fem. of Latin riparius "of a riverbank" (see riparian). The Old English word was ea "river," cognate with Gothic ahwa, Latin aqua (see aqua-).

U.S. slang phrase up the river "in prison" (1891) is originally in reference to Sing Sing prison, which was literally "up the (Hudson) river" from New York City. Phrase down the river "done with" perhaps echoes sense in to sell down the river (1851), originally of troublesome slaves, to sell from the Upper South to the harsher cotton plantations of the Deep South.
riverine (adj.): 1860, from river + -ine (1).
rivet (n.): c.1400, from Old French rivet, possibly from Middle Dutch wriven "turn, grind." The English word may be directly from Middle Dutch.
rivet (v.): early 15c., from rivet (n.). Meaning "to command the attention" is from c.1600. Related: Riveted; riveting.
riveting (adj.): "commanding attention," 1854, present participle adjective from rivet (v.).
Riviera: "Mediterranean seacoast around Genoa," 1630s, from Italian riviera, literally "bank, shore" (see river). In extended use, the coast from Marseilles to La Spezia, which became popular 19c. as a winter resort.
rivulet (n.): 1580s, from Italian rivoletto, diminutive of rivolo, itself a diminutive, from Latin rivus "stream, brook," from PIE *reiwos, literally "that which flows," from root *reie- "to flow, run" (see Rhine).
RNA (n.): 1948, abbreviation of ribonucleic acid (see ribonucleic).
roach (n.1): 1837, shortened form of cockroach, in contemporary writing said to be from a polite desire to avoid the sexual connotation in the first syllable; meaning "butt of a marijuana cigarette" is first recorded 1938, perhaps from resemblance to the insect, but perhaps a different word entirely.
roach (n.2): small freshwater fish, early 14c., from Old French roche (13c.), perhaps from a Germanic source.
road (n.): Old English rad "riding, hostile incursion," from Proto-Germanic *ridanan, source of Old English ridan (see ride). Also related to raid. In Middle English, "a riding, a journey;" sense of "open way for traveling between two places" is first recorded 1590s. Modern spelling established 18c.

Road test is from 1906. Road hog is attested from 1886; road rage is from 1988. Road map is from 1786; road trip is by 1950, originally of baseball teams.