Online Etymology Dictionary

-rama: noun suffix meaning "spectacular display or instance of," 1824, abstracted from panorama, ultimately from Greek horama "sight."
-re: phonetic spelling change from -re to -er in words such as fibre, centre, theatre in U.S. began late 18c.; under urging of Noah Webster (1804 edition of his speller, and especially the 1806 dictionary), it was established over the next 25 years. The -re spelling, like -our, however, had the authority of Johnson's dictionary behind it and remained in Britain, where it came to be a point of national pride, contra the Yankees.

Despite Webster's efforts, -re was retained in words with -c- or -g- (e.g. ogre, acre, the latter of which Webster insisted to the end of his days ought to be aker, and it was so printed in editions of the dictionary during his lifetime). The -re spelling generally is more justified by conservative etymology, based on French antecedents. It is met today in the U.S. only in Theatre in the proper names of entertainment showplaces, where it is perhaps felt to coax a perception of high class.
-rel: also -erel, diminutive or depreciatory suffix, in some cases from Old French -erel (Modern French -ereau) or -erelle, but in most cases used with native stems.
-ry: reduced form of -ery.
R: In a circle, meaning "registered (trademark)," first incorporated in U.S. statues 1946. Three Rs (1825) said to have been given as a toast by Sir W. Curtis (1752-1829). R&R "rest and relaxation," first recorded 1953, American English; R&B "rhythm and blues" (type of popular music) first attested 1949, American English.
R.A.F.: also RAF, initialism for Royal Air Force, founded 1918 by consolidation of Royal Flying Corps and Royal Naval Air Service.
R.E.M.: also REM, 1957, initialism for rapid eye movement.
R.O.T.C.: also ROTC, 1916, American English, initialism for Reserve Officers' Training Corps, established as part of the National Defense Act of 1916.
R.S.V.P.: also RSVP, c.1845, from French, abbreviation of répondez, s'il vous plait "reply, if you please."
rabbet (n.): "rectangular groove cut in a piece of timber," late 14c., from Old French rabbat "a recess in a wall," literally "a beating down," from rabattre "beat down, beat back" (see rebate (v.)). The verb is attested from 1560s.
rabbi (n.): "Jewish doctor of religious law," late 15c. (in Old English in biblical context only; in Middle English also as a title prefixed to personal names), from Late Latin rabbi, from Greek rhabbi, from Mishnaic Hebrew rabbi "my master," from rabh "master, great one," title of respect for Jewish doctors of law + -i, first person singular pronominal suffix. From Semitic root r-b-b "to be great or numerous" (cf. robh "multitude;" Arabic rabba "was great," rabb "master").

The -n- in rabbinical (1620s) is via French form rabbin, from Medieval Latin rabbinus (cf. Italian rabbino, Spanish, Portuguese rabino), perhaps from a presumed plural of the Hebrew word.
rabbit (n.): late 14c., "young of the coney," from French dialect (cf. Walloon robète), diminutive of Flemish or Middle Dutch robbe "rabbit," of unknown origin. "A Germanic noun with a French suffix" [Liberman]. The adult was a coney (q.v.) until 18c.
Zoologically speaking, there are no native rabbits in the United States; they are all hares. But the early colonists, for some unknown reason, dropped the word hare out of their vocabulary, and it is rarely heard in American speech to this day. When it appears it is almost always applied to the so-called Belgian hare, which, curiously enough, is not a hare at all, but a true rabbit. [H.L. Mencken]
Rabbit punch "chop on the back of the neck" so called from resemblance to a gamekeeper's method of dispatching an injured rabbit. Pulling rabbits from a hat as a conjurer's trick recorded by 1843. Rabbit's foot "good luck charm" first attested 1879, in U.S. Southern black culture. Earlier references are to its use as a tool to apply cosmetic powders.
[N]ear one of them was the dressing-room of the principal danseuse of the establishment, who was at the time of the rising of the curtain consulting a mirror in regard to the effect produced by the application of a rouge-laden rabbit's foot to her cheeks, and whose toilet we must remark, passim, was not entirely completed. ["New York Musical Review and Gazette," Nov. 29, 1856]
rabble (n.): c.1300, "pack of animals," possibly related to Middle English rablen "speak in a rapid, confused manner," probably imitative of hurry and confusion (cf. Middle Dutch rabbelen, Low German rabbeln "to chatter"). Meaning "tumultuous crowd of people" is first recorded 1510s; applied contemptuously to the common or low part of any populace from 1550s. Rabble-rousing first attested 1802 in Sydney Smith.
Rabelaisian (adj.): 1817, from French author François Rabelais (c.1490-1553), whose writings "are distinguished by exuberance of imagination and language combined with extravagance and coarseness of humor and satire." [OED]
rabid (adj.): 1610s, "furious, raving," from Latin rabidus, from rabere "be mad, rave" (see rage). Meaning "made mad by rabies" first recorded 1804. Related: Rabidly; rabidness.
rabies (n.): 1590s, from Latin rabies "madness, rage, fury," related to rabere "be mad, rave" (see rage). Sense of "madness in dogs" was a secondary meaning in Latin.
raccoon (n.): also racoon, c.1600, arocoun, from Algonquian (Powhatan) arahkun, from arahkunem "he scratches with the hands." Early forms included Capt. John Smith's raugroughcum. In Norwegian, vaskebjørn, literally "wash-bear."
race (n.1): "act of running," c.1300, from Old Norse ras "running, rush (of water)," cognate with Old English ræs, which became Middle English resen "attack, incursion," but did not survive into Modern English. Both the Norse and Old English words are from Proto-Germanic *ræs- (cf. Middle Dutch rasen "to rave, rage," German rasen). Originally a northern word, it became general in English c.1550. Meaning "contest of speed" first recorded 1510s. Race-horse is from 1620s.

Meaning "strong current of water" is from late 14c., possibly influenced by Old French raz, which had a similar meaning, and which probably is from Breton raz "a strait, narrow channel;" this French source also may have given race its meaning of "channel of a stream" (especially an artificial one to a mill), recorded from 1560s.
race (n.2): "people of common descent," c.1500, from Middle French razza "race, breed, lineage," possibly from Italian razza, of unknown origin (cf. Spanish and Portuguese raza).

Original senses in English included "wines with characteristic flavor" (1520), "group of people with common occupation" (c.1500), and "generation" (c.1560). Meaning "tribe, nation, or people regarded as of common stock" is from c.1600. Modern meaning of "one of the great divisions of mankind based on physical peculiarities" is from 1774 (though even among anthropologists there never has been an accepted classification of these).
Just being a Negro doesn't qualify you to understand the race situation any more than being sick makes you an expert on medicine. [Dick Gregory, 1964]
Klein suggests these derive from Arabic ra's "head, beginning, origin" (cf. Hebrew rosh). Old English þeode meant both "race" and "language;" as a verb, geþeodan, it meant "to unite, to join." Race-riot attested from 1889, American English.
race (v.): 1670s, from race (n.1). In reference to an engine, from 1862. Related: Raced; racing.
raceme (n.): 1785, from Latin racemus "a cluster of grapes" (see raisin).
Rachel: fem. proper name, biblical daughter of Laban, wife of Jacob, from Late Latin, from Greek Hrakhel, from Hebrew Rahel, literally "ewe" (cf. Arabic rahil, Aramaic rahla).
rachitic (adj.): 1797, from rachitis, Modern Latin, from Greek rhakhitis, from rhakhis "spine, ridge, rib of a leaf."
racial (adj.): 1862, from race (n.2) + -ial. Related: Racially.
racialization (n.): 1874, from racial + -ize + -ation.
racism (n.): 1936; see racist.
racist: 1932 as a noun, 1938 as an adjective, from race (n.2); racism is first attested 1936 (from French racisme, 1935), originally in the context of Nazi theories. But they replaced earlier words, racialism (1871) and racialist (1917), both often used early 20c. in a British or South African context.
rack (n.1): "frame with bars," c.1300, possibly from Middle Dutch rec "framework," related to recken "stretch out," cognate with Old English reccan "to stretch out," from Proto-Germanic *rakjanan (cf. Old Norse rekja, Old Frisian reza, Old High German recchen, German recken, Gothic uf-rakjan "to stretch out").

Meaning "instrument of torture" first recorded mid-15c. (verb meaning "to torture on the rack" is from early 15c.), perhaps from German rackbank, originally an implement for stretching leather, etc. Figurative sense of "agony" is from 1590s. Mechanical meaning "toothed bar" is from 1797 (see pinion). Meaning "set of antlers" is first attested 1945, American English; hence slang sense of "a woman's breasts" (especially if large), by 1991. Off the rack in reference to clothing is from 1951.
rack (n.2): "gait of a horse," 1520s (implied in racking), perhaps from French racquassure "racking of a horse in his pace," of unknown origin. Or perhaps a variant of rock (v.1).
rack (n.3): "clouds driven before the wind," c.1300, also "rush of wind, collision, crash," possibly from Old English racu "cloud," reinforced by Old Norse rek "wreckage, jetsam," or by influence of Old English wræc "something driven." Originally a northern word, perhaps from an unrecorded Scandinavian cognate of Old English racu. Often confused with wrack (q.v.), especially in phrase rack and ruin (1590s). The distinction is that rack is "driven clouds;" wrack is "seaweed cast up on shore."
rack (v.): "to sleep," teen-ager slang, 1960s, from rack (n.1) (rack was Navy slang for "bed" in 1940s). Related: Racked; racking. Rack up "register accumulate, achieve" is first attested 1943 (in "Billboard"), probably from method of keeping score in pool halls.
racket (n.1): "loud noise," 1560s, said to be imitative. Meaning "dishonest activity" (1785) is perhaps from racquet, via notion of "game," reinforced by rack-rent "extortionate rent" (1590s), from rack (n.1).
racket (n.2): "bat used in tennis, etc.," see racquet.
racketeer: 1928 (noun and verb), from racket (n.1) + -eer. Related: Racketeering.
raconteur (n.): 1828, from French raconteur, from raconter "to recount," from re- (see re-) + Old French aconter "to count, render account" (see account (v.); and cf. recount (v.1)).
racquet (n.): c.1500, "device used in tennis, etc.," probably originally "tennis-like game played with open hand" (late 14c.), from French requette "racket, palm of the hand," perhaps via Italian racchetta or Spanish raqueta, both from Arabic rahat, a form of raha "palm of the hand."
racquetball (n.): 1972, from racquet + ball (n.1).
racy (adj.): 1650s, "having a characteristic taste" (of wines, fruits, etc.), from race (n.2) in its older sense of "flavor" + -y (2); meaning "having a quality of vigor" (1660s) led to that of "improper, risqué," first recorded 1901, probably reinforced by phrase racy of the soil "earthy" (1870).
rad: "x-ray dose unit," 1918, shortened form of radiation (q.v.). As shortened form of radical (n.), it is attested in political slang from 1820. Teen slang sense of "extraordinary, wonderful" is from late 1970s (see radical).
radar: 1941, acronym (more or less) for radio detecting and ranging. The U.S. choice, it won out over British radiolocation.
radial (adj.): 1560s, from Medieval Latin radialis, from Latin radius "beam of light" (see radius). As a type of tire, attested from 1965, short for radial-ply (tire).
radian: 1879, from radius.
radiance (n.): c.1600, "brilliant light," from Medieval Latin radiantia "brightness," from radiare "to beam, shine" (see radiant). Figurative use from 1761.
radiant (adj.): mid-15c., from Middle French radiant, from Latin radiantem (nominative radians) "shining," present participle of radiare "to beam, shine" (see radiation). Of beauty, etc., first attested c.1500.
radiate (v.): 1610s, from Latin radiatus, past participle of radiare "to beam, shine" (see radiation). Related: Radiated; radiates; radiating.
radiation (n.): 1550s, from Latin radiationem (nominative radiatio) "a shining, radiation," noun of action from radiare "to beam, shine," from radius "beam of light" (see radius).
radiator (n.): 1836, "any thing that radiates," agent noun in Latin form from radiate. Meaning "heater" is from 1851; sense of "cooling device in internal combustion engine" is 1900.
radical (adj.): late 14c., in a medieval philosophical sense, from Late Latin radicalis "of or having roots," from Latin radix (genitive radicis) "root" (see radish). Meaning "going to the origin, essential" is from 1650s. Political sense of "reformist" (via notion of "change from the roots") is first recorded 1802 (n.), 1817 (adj.), of the extreme section of the British Liberal party (radical reform had been a current phrase since 1786); meaning "unconventional" is from 1921. U.S. youth slang use is from 1983, from 1970s surfer slang meaning "at the limits of control." Radical chic is attested from 1970; popularized, if not coined, by Tom Wolfe.
radical (n.): 1802, in the political sense, from radical (adj.).
radicalism (n.): 1820, from radical + -ism.