Online Etymology Dictionary

roseate (adj.): 1580s, from Latin roseus (see rose) + -ate.
rosemary (n.): mid-15c., earlier rosmarine (c.1300), from Latin rosmarinus, literally "dew of the sea" (cf. French romarin), from ros "dew" + marinus (see marine). Perhaps so called because it grew near coasts. Form altered in English by influence of rose and Mary.

Latin ros is from PIE *ras-/*eras- "to flow, wet, moisten" (cf. Lithuanian rasa, Old Church Slavonic rosa "dew," Sanskrit rasah "sap, juice, fluid, essence," Hittite arszi "flows," and perhaps also Rha, Scythian name of the River Volga (see rhubarb)).
Rosetta Stone (n.): discovered 1798 at Rosetta, Egypt; now in British Museum. Dating to 2c. B.C.E., its trilingual inscription helped Jean-François Champollion decipher Egyptian demotic and hieroglyphics in 1822, which opened the way to study of all early Egyptian records. Hence, figurative use of the term to mean "something which provides the key to previously unattainable understanding" (1902).
rosette (n.): "a rose-shaped ornament," especially a bunch or knot of ribbons worn as a decoration, 1790, from French rosette, diminutive of rose "rose" (see rose).
Rosh Hashanah (n.): Jewish new year, 1846, from Hebrew rosh hashshanah, literally "head of the year," from rosh "head of" + hash-shanah "the year."
Rosicrucian: 1620s (n.), 1660s (adj.), from Modern Latin rosa crucis (DuCange) or crux, Latinization of German Rosenkreuz, French rosecroix, from the secret society's reputed founder Christian Rosenkreuz, said to date from 1484, but not mentioned before 1614.
rosin (n.): mid-14c., from Old French raisine, variant of résine (see resin). The verb is from late 15c.
roster (n.): 1727, from Dutch rooster "table, list," originally "gridiron," from Middle Dutch roosten "to roast" (see roast). So called from the grid of lines drawn on a paper to make a list.
rostral (adj.): c.1400, from Late Latin rostralis, from Latin rostrum "beak" (see rostrum).
rostrum (n.): 1540s, from Latin rostrum, name of the platform stand for public speakers in the Forum in ancient Rome. It was decorated with the beaks of ships taken in the first naval victory of the Roman republic, over Antium, in 338 B.C.E., and the word's older sense is "end of a ship's prow," literally "beak, muzzle, snout," originally "means of gnawing," instrument noun form of rodere "to gnaw" (see rodent). Cf. claustrum "lock, bar," from claudere "to shut." Extended sense of any platform for public speaking is first recorded 1766. Classical plural form is rostra.
rosy (adj.): late 14c., of a color, from rose (n.) + -y (2). From 1590s of healthy complexions; 1775 in the sense "cheerful;" meaning "promising" is from 1887.
rot (v.): Old English rotian "to decay," from Proto-Germanic *rutjan (cf. Old Saxon roton, Old Norse rotna, Old Frisian rotia, Middle Dutch roten, Old High German rozzen "to rot," German rößen "to steep flax"), from stem *rut-. The noun (c.1300) probably is of Scandinavian origin (cf. Icelandic rot, Swedish röta, Danish røde "decay, putrefaction"), and is related to the verb. Slang noun sense of "rubbish, trash" is from 1848.
rotary (adj.): 1731, from Medieval Latin rotarius "pertaining to wheels," from Latin rota "wheel," from PIE root *roto- "to run, to turn, to roll" (cf. Sanskrit rathah "car, chariot;" Avestan ratho; Lithuanian ratas "wheel," ritu "I roll;" Old High German rad, German Rad, Dutch rad, Old Frisian reth, Old Saxon rath, Old Irish roth, Welsh rhod "carriage wheel"). The international service club (founded by Paul P. Harris in Chicago in 1905) so called from the practice of clubs entertaining in rotation. Hence Rotarian (1911).
rotate (v.): 1794, back-formation from rotation. Related: Rotated; rotating.
rotation (n.): 1550s, from Latin rotationem (nominative rotatio), noun of action from past participle stem of rotare "revolve, roll," from PIE *roto- (see rotary). Rotator "muscle which allows a part to be moved circularly" is recorded from 1670s.
rotavirus (n.): 1974, wheel-shaped virus causing inflammation of the lining of the intestines, from Latin rota "wheel" (see rotary) + virus.
rote (n.): c.1300, in phrase bi rote "by heart," of uncertain origin, sometimes said to be connected with Old French rote "route" (see route), or from Latin rota "wheel" (see rotary), but OED calls both suggestions groundless.
rotgut (n.): also rot-gut, "unwholesome liquor," 1630s, from rot (v.) + gut (n.).
Rothschild: "rich person," 1833, in reference to the international banking family descended from Mayer Amschel Rothschild (1744-1812) of Frankfurt. The surname is literally "red shield," a house name.
rotifera (n.): "class of microscopic freshwater organisms," 1830, Modern Latin, from Latin rota "wheel" (see rotary) + -fer "bearing" (see bear (v.)). The animalcules use rotary organs to swim about.
rotisserie (n.): 1868, "restaurant where meat is roasted on a spit," from French rôtisserie "shop selling cooked food, restaurant," from present participle stem of rôtir "to roast," from Old French rostir (see roast). As an in-home cooking apparatus, attested from 1953. Manufacturers (or their copy writers) back-formed a verb, rotiss (1958). Rotisserie league (1980), a form of fantasy baseball, is based on La Rotisserie, the Manhattan restaurant where it was conceived.
rotogravure (n.): 1913, from German Rotogravur (originally, in full, Deutsche Tiefdrück Gesellschaft), said to blend two corporate names, Rotophot and Deutsche Photogravur A.G. Etymologically, the roots are Latin rota "wheel, roller" (see rotary) and French gravure "engraving" (see gravure). The process was used for printing photo sections of newspapers and magazines, so that the word came to be used for these.
rotor (n.): 1873, irregular shortening of rotator, originally in mathematics. Mechanical sense is attested from 1903; specifically of helicopters from 1930.
rototiller (n.): 1923, from roto-, from Latin rota "wheel" (see rotary) + tiller.
rotten (adj.): early 13c., from Old Norse rotinn "decayed," past participle of verb related to rotna "to decay," from Proto-Germanic stem *rut- (see rot). Sense of "corrupt" is from late 14c.; weakened sense of "bad" first recorded 1881. Rotten apple is from a saying traced back to at least 1528: "For one rotten apple lytell and lytell putrifieth an whole heape."
rotter (n.): "person deemed objectionable on moral grounds," 1889, slang, from rot + -er (3).
Rottweiler (n.): 1907, from Rottweil, town in Württemberg, southern Germany.
rotund (adj.): 1705, from Latin rotundus "round, circular, like a wheel," from rota "wheel" (see rotary). Meaning "full-toned style of oratory" (1830) is after Horace's ore rotundo in "Poetics."
rotunda (n.): "round building," 1680s, from Italian rotonda, especially the Pantheon, from Latin rotunda, fem. of rotundus "round" (see rotund). Meaning "circular hall or room within a building" is from 1780.
rotundity (n.): 1580s, from Latin rotunditas, from rotundus "round" (see rotund).
roue (n.): 1800, from French roué "dissipated man, rake," originally past participle of Old French rouer "to break on the wheel," from Latin rotare "roll;" said to have been first applied in French c.1720 to dissolute friends of the Duke of Orleans (regent of France 1715-23), to suggest the punishment they deserved.
rouge (n.): 1753, in cosmetic sense, from French rouge "red coloring matter," noun use of adjective "red," from Latin rubeus, related to ruber "red" (see red). Replaced native paint in this sense. The verb is attested from 1777.
rough (n.): late 15c., "broken ground," from rough (adj.). Specific sense in golf is from 1901. Phrase in the rough first recorded 1823. Meaning "a rowdy" is first attested 1837.
rough (adj.): Old English ruh "rough, untrimmed, uncultivated," from West Germanic *rukhwaz "shaggy, hairy, rough" (cf. Middle Dutch ruuch, Dutch ruig, Old High German ruher, German rauh), from Proto-Germanic *rukhaz. The original -gh- sound was guttural, as in Scottish loch. Sense of "approximate" is first recorded c.1600. Rough draft is from 1690s. Rough-and-ready is from 1810, originally military; rough-and-tumble (1810) is from the prize ring.
rough (v.): late 15c., from rough (adj.). Phrase rough it (1768) is originally nautical; to rough (someone) up is from 1868. Related: Roughed; roughing. The U.S. football penalty roughing was originally a term from boxing (1866).
rough rider (n.): 1733, "horse-breaker," from rough (adj. or adv.) + rider. In specific military use, a non-commissioned officer in cavalry regiments from 1802; meaning "irregular cavalryman" is attested from 1884.
rough-house (n.): 1887, "uproar, disturbance," from rough (adj.) + house. The verb is first attested 1896.
roughage (n.): 1883, "rough grass or weeds," from rough + -age. Meaning "coarse, bulky food" first recorded 1927.
roughneck (n.): also rough-neck, 1836, "rugged individual," from rough (adj.) + neck (n.). Original context is the Texas frontier, later adpoted to labor organization toughs. Specific sense of "oil rig worker" is recorded from 1917.
roughshod (adj.): also rough-shod, 1680s, from rough (adj.) + shod. originally from horses shod with the nails projecting from the shoe, to prevent slipping.
roulette (n.): 1734, "small wheel," from French roulette "gambling game played with a revolving wheel," literally "small wheel," from Old French roelete "little wheel," on model of Late Latin rotella, diminutive of Latin rota "wheel" (see rotary). The game of chance so-called from 1745.
round (adj., adv.): late 13c., from Anglo-French rounde, Old French roont, probably originally *redond, from Vulgar Latin *retundus (cf. Provençal redon, Spanish redondo, Old Italian ritondo), from Latin rotundus "like a wheel, circular, round," related to rota "wheel" (see rotary). In many uses it is a shortened form of around. The French word is the source of Middle Dutch ront (Dutch rond), Middle High German runt (German rund) and similar Germanic words.

First record of round trip is from 1844, originally of railways. Round number is 1640s, from earlier sense of "full, complete" (mid-14c., sense of symmetry extended to that of completeness). Round heels attested from 1926, in reference to incompetent boxers, 1927 in reference to loose women, in either case implying an inability to avoid ending up flat on one's back.
round (n.): early 14c., "a spherical body," from round (adj.). Cf. Dutch rond, Danish and Swedish rund, German runde, all nouns from adjectives. Meaning "large round piece of beef" is recorded from 1650s. Theatrical sense (in phrase in the round) is recorded from 1944. Sense of "circuit performed by a sentinel" is from 1590s; that of "recurring course of time" is from 1710. Meaning "song sung by two or more, beginning at different times" is from 1520s. Golfing sense attested from 1775. Meaning "quantity of liquor served to a company at one time" is from 1630s; that of "single bout in a fight or boxing match" is from 1812; "single discharge of a firearm" is from 1725. Sense of "recurring session of meetings or negotiations" is from 1964.
round (v.): late 14c., "to make round," from round (adj.). Meaning "to approximate a number" is from 1934. Related: Rounded; rounding.
round robin (n.): "petition or complaint signed in a circle to disguise the order in which names were affixed and prevent ringleaders from being identified," 1730, originally in reference to sailors and frequently identified as a nautical term. As a kind of tournament in which each player plays the others, it is recorded from 1895.
roundabout (adv.): "by a circuitous route," 1870, from round (adv.) + about. Noun sense of "traffic circle" is attested from 1927.
roundel (n.): late 13c., "a circle," from Old French rondel, from rond "round" (see round (n.)).
roundelay (n.): 1570s, from Middle French rondelet, diminutive of rondel "short poem with a refrain," literally "small circle," from Old French rondel, diminutive of rond "circle, sphere," originally an adjective from roont (see round). Spelling developed by association with lay (n.) "poem to be sung."
rounder (n.): 1620s, "a sentinel," agent noun from round (n.) on notion of "one who makes the rounds." Sense of "chronic drunkard or criminal" is from 1854, on notion of one who is habitually in and out of jails or bars.
Roundhead (n.): "adherent of Parliamentary party in the English Civil War," 1641, so called for their custom of wearing the hair close-cropped, in contrast to the flowing curls of the cavaliers.