Online Etymology Dictionary

rhetorical (adj.): late 15c., "eloquent," from Latin rhetoricus (see rhetoric). Meaning "pertaining to rhetoric" is from 1520s. Rhetorical question is from 1670s. Related: Rhetorically.
rhetorician (n.): early 15c., Old French rethoricien, from Latin rhetoricus (see rhetoric).
rheum (n.): late 14c., from Old French reume (13c.), ultimately from Greek rheuma "stream, current, a flowing," from rhein "to flow," from PIE root *sreu- "to flow" (cf. Sanskrit sravati "flows," srotah "stream;" Avestan thraotah- "stream, river," Old Persian rauta "river;" Greek rheos "a flowing, stream," rhythmos "rhythm," rhytos "fluid, liquid;" Old Irish sruaim, Irish sruth "stream, river;" Welsh ffrwd "stream;" Old Norse straumr, Old English stream, Old High German strom (second element in maelstrom); Lettish strauma "stream, river;" Lithuanian sraveti "to trickle, ooze;" Old Church Slavonic struja "river," o-strovu "island," literally "that which is surrounded by a river;" Polish strumień "brook").
rheumatic (adj.): late 14c., from Old French reumatique, from Latin rheumaticus "troubled with rheum," from Greek rheumatikos, from rheuma (see rheum).
rheumatism (n.): c.1600, from Late Latin rheumatismus, from Greek rheumatismos, from rheumatizein, from rheuma (see rheum). "Formerly supposed to be caused by a 'defluxion of rheum.'" [OED]
rheumatoid (adj.): 1847, from Greek rheumat-, stem of rheuma (see rheum) + -oid.
rheumatology (n.): 1949, from Greek rheumat-, from rheuma (see rheum) + -ology. Related: Rheumatologist.
rheumy (adj.): 1590s, from rheum + -y (2).
Rhine: principal river in western Germany, from German Rhein, from Middle High German Rin, ultimately from Gaulish Renos, literally "that which flows," from PIE root *reie- "to move, flow, run" (cf. Sanskrit rinati "causes to flow," ritih "stream, course;" Latin rivus "stream;" Old Church Slavonic reka "river;" Middle Irish rian "river, way;" Gothic rinnan "run, flow," rinno "brook;" Middle Low German ride "brook;" Old English riþ "stream;" Old English rinnan, Old Norse rinna "to run," Dutch ril "running stream"). The spelling with -h- (cf. Latin Rhenus; French Rhin) is from influence of the Greek form of the name, Rhenos.
rhinestone (n.): 1879, a loan-translation of French caillou du Rhin "Rhine pebble," so called because they were made near Strasburg, on the River Rhine.
Rhinestone jewelry, a reproduction of the ornaments of the Louis XV. period, is all the rage in Paris. The Rhinestones are as brilliant as diamonds, and being set in silver, will stand any amount of wear or of cleaning. ["The American Stationer," March 20, 1879]
rhinitis (n.): 1829, from Greek rhin-, from rhis "nose" + -itis.
rhino (n.): slang for "cash," 1680s, of unknown origin.
rhinoceros (n.): c.1300, from Latin rhinoceros, from Greek rhinokeros, from rhinos "nose" (a word of unknown origin) + keras "horn" (see kerato-). Shortened form rhino is first attested 1884.
What is the plural of rhinoceros? ... Well, Liddell and Scott seem to authorize 'rhinocerotes,' which is pedantic, but 'rhinoceroses' is not euphonious. [Sir Charles Eliot, "The East Africa Protectorate," 1905]
rhinoplasty (n.): 1828, earlier rhinoplastic (1823), from comb. form of Greek rhinos "nose" + -plastia, from plastos "molded, formed" (see plastic).
rhinorrhea (n.): 1866, from Greek rhin-, from rhis "nose" + rhoia "flow" (see rheum).
rhizoid (adj.): 1858, from Greek rhiza "root" (see rhizome) + -oid (see -oid).
rhizome (n.): 1832, from Greek rhizoma "mass of tree roots," from rhizoun "cause to strike root," from rhiza "root," probably from PIE *wrad- "branch, root" (cf. Latin radix "root," Old Norse rot "root," Old English wyrt "plant, herb;" see radish).
Rhode Island: U.S. state, the region is traditionally said to have been named by Italian explorer Giovanni da Verrazzano when he passed through in 1524, based on an imagined similarity between modern Block Island and the Greek Isle of Rhodes. More likely from Roodt Eylandt, the name Dutch explorer Adriaen Block gave to Block Island c.1614, literally "red island," so called for the color of its soil. Under this theory, the name was altered by 17c. English settlers by influence of the Greek island name, and then extended to the mainland part of the colony. Block Island later (by 1685) was renamed for the Dutch explorer.
Rhodes scholar: holder of any of the scholarships founded at Oxford in 1902 by British financier and imperialist Cecil Rhodes (1853-1902), for whom the former African nation of Rhodesia also was named.
rhodium (n.): hard white metallic element, 1804, named for the color of solutions containing it, from Greek rhodon "rose" (see rose (n.)) + metallic element ending -ium.
rhododendron (n.): c.1600, from Latin rhododendron, from Greek rhododendron, literally "rose-tree," from rhodon "rose" (see rose) + dendron "tree" (see dendro-).
rhomboid: 1560s (n.); 1690s (adj.), from French rhomboide or directly from Late Latin rhomboides, from Greek rhomboeides; see rhombus + -oid. Related: Rhomboidal.
rhombus (n.): 1560s, from Late Latin rhombus, from Greek rhombos "rhombus, spinning top," from rhembesthai "to spin, whirl," from PIE *wrembh-, from *werbh- "to turn, twist, bend" (cf. Old English weorpan "to throw away"), from root *wer- (3) "to turn, bend" (see versus).
rhonchi: plural of rhonchus (1829), from Greek rhenkhos "snoring."
rhotacism (n.): 1830, from Modern Latin rhotacismus, from Greek rhotakizein, from rho "the letter -r-," from Hebrew or Phoenician roth. Excessive or peculiar use of the -r- sound (cf. the "burr"), especially the conversion of another sound (usually -s-) to -r-.
rhubarb (n.): late 14c., from Old French rubarbe, from Medieval Latin rheubarbarum, from Greek rha barbaron "foreign rhubarb," from rha "rhubarb" (associated with Rha, ancient Scythian name of the River Volga) + barbaron, neuter of barbaros "foreign."

Grown in China and Tibet, it was imported into ancient Europe by way of Russia. Spelling altered in Medieval Latin by association with rheum. European native species so called from 1640s. Baseball slang meaning "loud squabble on the field" is from 1938, of unknown origin, said to have been first used by broadcaster Garry Schumacher. Perhaps connected with use of rhubarb as a word repeated by stage actors to give the impression of hubbub or conversation (attested from 1934).
rhyme (n.): "agreement in terminal sounds," 1560s, partially restored spelling, from Middle English ryme, rime (c.1200) "measure, meter, rhythm," later "rhymed verse" (mid-13c.), from Old French rime (fem.), related to Old Provençal rim (masc.), earlier *ritme, from Latin rithmus, from Greek rhythmos "measured motion, time, proportion" (see rhythm).
In MedL. rithmus was used of accentual, as opposed to quantitative, verse, and, as accentual verse was usually rhymed, the word acquired the meaning which it has in all the Rom[anic]. and Teut[onic] langs. [Weekley]
Persistence of older form is due to popular association with Old English rim "number," from PIE root *re(i)- "to reason, count." Paired with reason since at least late 15c. Phrase rhyme or reason "good sense" (chiefly used in the negative) is from 1660s. Rhyme scheme is attested from 1931. Rhyme royal (1841) is a stanza of seven 10-syllable lines rhymed a-b-a-b-b-c-c.
rhyme (v.): "make verses, make rhymes," c.1300, rimen, from Old French rimer, from rime "verse" (see rhyme (n.)). Attested 1670s (of words) in sense "to have the same end sound." Related: Rhymed; rhyming.
rhythm (n.): 1550s, from Latin rhythmus "movement in time," from Greek rhythmos "measured flow or movement, rhythm," related to rhein "to flow," from PIE root *sreu- "to flow" (see rheum). In Medieval Latin, rithmus was used for accentual, as opposed to quantitative, verse, and accentual verse was usually rhymed. Rhythm method of birth control attested from 1936. Rhythm and blues, U.S. music style, is from 1949 (first in "Billboard").
rhythmic (adj.): 1560s, from French rhythmique or directly from Latin rhythmicus, from Greek rhythmikos, from rhythmos (see rhythm). Related: Rhythmical; rhythmically.
ria (n.): from Spanish ria "estuary," adopted as a geological term first in German, 1886.
rialto (n.): 1879, "exchange, mart," from the Rialto of Venice, the name of the quarter where the exchange was situated, contracted from Rivoalto and named for the canal (Latin rivus altus "deep stream") which it crosses.
riata (n.): 1846, from Spanish reata (see lariat).
rib (n.): Old English ribb "rib," from Proto-Germanic *rebja- (cf. Old Norse rif, Old Frisian ribb, Old High German ribba, German Rippe), literally "a covering" (of the chest), from PIE *rebh- "to roof, cover" (cf. Old Church Slavonic rebro "rib"). Rib joint "brothel" is slang from 1943, probably in reference to Adam's rib (cf. rib "woman, wife," attested from 1580s).
rib (v.): "tease, fool," 1930, apparently from rib (n.); perhaps as a figurative suggestion of poking someone in the ribs. Related: Ribbed; ribbing.
ribald (n.): mid-13c., "a rogue, ruffian, rascall, scoundrell, varlet, filthie fellow" [Cotgrave], from Old French ribalt, of uncertain origin, perhaps from riber "be wanton, sleep around," from a Germanic source (cf. Old High German riban "be wanton," literally "to rub," possibly from the common euphemistic use of "rub" words to mean "have sex"), from Proto-Germanic *wribanan, from PIE root *wer- (3) "to turn, bend" (see versus). The adjective is attested from c.1500, from the noun.
ribaldry (n.): 14c., from Old French rebauderie, from ribalt (see ribald).
ribbon (n.): late 14c., ribane, from Old French riban "a ribbon," variant of ruban (13c.), of unknown origin, possibly from a Germanic compound whose second element is related to band. Modern spelling is from mid-16c. Custom of colored ribbon loops worn on lapels to declare support for some group perceived as suffering or oppressed began in 1991 with AIDS red ribbons.
riboflavin (n.): "growth-promoting substance known as vitamin B2," 1935, from German Riboflavin (1935), from comb. form of ribose (q.v.) + flavin, from Latin flavus "yellow" (see blue); so called from its color. Also sometimes known as lactoflavine, as it is found in milk.
ribonucleic (adj.): 1931, from ribo-, from ribose (q.v.), the sugar component, + nucleic acid.
ribose: 1892, from German Ribose (1891), shortened and arbitrarily rearranged from English arabinose (c.1880), a sugar which is so called because it is formed from gum arabic.
ribosome (n.): 1958, coined by U.S. microbiologist Richard B. Roberts (1910-1980) from ribo(nucleic acid) + -some "body."
rice (n.): mid-13c., from Old French ris, from Italian riso, from Latin oriza, from Greek oryza "rice," via an Indo-Iranian language (cf. Pashto vrize, Old Persian brizi), ultimately from Sanskrit vrihi-s "rice." The Greek word is the ultimate source of all European words (Welsh reis, German reis, Lithuanian rysai, Serbo-Croatian riza, Polish ryż, etc.). Introduced 1647 in the Carolinas. Rice paper (1822) is made from a reed found in Taiwan.
rich (adj.): Old English rice "wealthy, powerful, mighty," from Proto-Germanic *rikijaz (cf. Old Norse rikr, Old High German rihhi "ruler, powerful, rich," Old Frisian rike, Dutch rijk, German reich "rich," Gothic reiks "ruler, powerful, rich"), borrowed from a Celtic source akin to Gaulish *rix, Old Irish ri (genitive rig) "king," from PIE root *reg- "move in a straight line," hence, "direct, rule" (see rex).

The form of the word influenced in Middle English by Old French riche "wealthy," from Frankish *riki "powerful," or some other cognate Germanic source. The evolution of the word reflects a connection between wealth and power in the ancient world. Of food and colors, from early 14c.; of sounds, from 1590s. Sense of "entertaining, amusing" is recorded from 1760. The noun meaning "the wealthy" was in Old English.
Richard: masc. proper name, Middle English Rycharde, from Old French Richard, from Old High German Ricohard, from Proto-Germanic *rik- "ruler" + *harthu "hard." One of the most popular names introduced by the Normans.
riches: "valued possessions, money, property," c.1200, modified from richesse (12c.), a singular form misunderstood as a plural, from Old French richesse "wealth, opulence," from riche. The Old French suffix -esse is from Latin -itia, added to adjectives to form nouns of quality (cf. duress, largesse).
Richter scale: 1938, devised by U.S. seismologist Charles Francis Richter (1900-1985).
ricin (n.): poison obtained from the castor-oil bean, 1896, from ricinus, genus name of the castor-oil plant (1694), from Latin ricinus (Pliny), perhaps the same word as ricinus "tick" (in sheep, dogs, etc.).
rick (n.): Old English hreac "stack of hay or straw," from Proto-Germanic *khraukaz (cf. Old Norse hraukr, Frisian reak, Dutch rook "heap"); perhaps related to ridge.
rickets (n.): disease caused by vitamin D deficiency, 1630s, of uncertain origin. Originally a local name for the disease in Dorset and Somerset, England. Some derive it from a Dorset word, rucket "to breathe with difficulty," but the sense connection is difficult. The Modern Latin name for the disease, rachitis, comes from Late Greek rhachitis "inflammation of the spine," from Greek rhakhis "spine," but this was chosen by Whistler for resemblance to rickets.