Online Etymology Dictionary

radically (adv.): c.1600, "thoroughly;" 1620s with reference to roots and origins, from radical (adj.) + -ly (2).
radicle (n.): 1670s, in botany, from Latin radicula, diminutive of radix (see radish).
radio (n.): "wireless transmission with radio waves," 1907, abstracted from earlier combinations such as radiophone (1881) and radio-telegraphy (1898), from radio-, comb. form of radiation (q.v.). Use for "radio receiver" is first attested 1913; sense of "sound broadcasting as a medium" is from 1913. Wireless remained more widespread until World War II, when military preference for radio turned the tables.
It is not a dream, but a probability that the radio will demolish blocs, cut the strings of red tape, actuate the voice "back home," dismantle politics and entrench the nation's executive in a position of power unlike that within the grasp of any executive in the world's history. ["The Reading Eagle," Reading, Pa., U.S.A., March 16, 1924]
radio (v.): 1919, from radio (n.). Related: Radioed; radioing.
radio-carbon (n.): "Carbon-14," 1940, from radio-, comb. form of radioactive, + carbon. Radio-carbon dating is attested from 1949.
radioactive (adj.): 1898, from French radio-actif, coined by Pierre and Marie Curie from radio-, comb. form of Latin radius (see radiation) + actif "active" (see active).
radioactivity (n.): 1899, from radioactive + -ity.
radiography (n.): 1896, from radio-, comb. form of radiation, + -graphy.
radioisotope (n.): 1946, from radio-, comb. form of radiation, + isotope.
radiolarian (n.): 1862, from Radiolaria, Modern Latin class name, from Latin radiolus, diminutive of radius (q.v.).
radiology (n.): "medical use of X-rays," 1900, from radio-, comb. form of radiation, + Greek-based scientific suffix -ology.
radiometric (adj.): 1877, from radio-, here indicating "radiant energy," + -metric. Radiometric dating attested from 1906.
radish (n.): late Old English rædic, from Latin radicem (nominative radix) "root," from PIE root *wrad- "twig, root" (cf. Greek rhiza, Lesbian brisda "root;" Greek hradamnos "branch;" Gothic waurts, Old English wyrt; Welsh gwridd, Old Irish fren "root").
radium (n.): radioactive metallic element, 1899, from French radium, named 1898 after identification by Marie Curie and her husband, formed in Modern Latin from Latin radius "ray" (see radius). So called for its power of emitting energy in the form of rays.
radius (n.): 1590s, "cross-shaft," from Latin radius "staff, spoke of a wheel, beam of light," of unknown origin. Perhaps related to radix "root," but Tucker suggests connection to Sanskrit vardhate "rises, makes grow," via root *neredh- "rise, out, extend forth;" or else Greek ardis "sharp point." The geometric sense first recorded 1610s. Plural is radii. Meaning "circular area of defined distance around some place" is attested from 1953. Meaning "shorter bone of the forearm" is from 1610s in English; it was used thus by Roman writer Aulus Cornelius Celsus (1c.).
radon (n.): heaviest gaseous element, 1918, from radium (q.v.) + -on suffix of inert gases. The element was identified in radioactive decay of radium. Alternative name niton (from Latin nitens "shining") gained currency in France and Germany.
radula (n.): 1753, from Latin radula "scraper, scraping iron," from radere "to scrape" (see raze).
raffia (n.): 1729, rofia, from Malagasy rafia. Modern form is attested from 1882; also raphia (1866).
raffish (adj.): "disreputable, vulgar," 1801 (first attested in Jane Austen), from raff "people," usually of a lower sort (1670s), probably from rif and raf (mid-14c.) "everyone," via French or Middle Dutch, ultimately also probably related to Swedish rafs "rubbish" (see riffraff).
raffle (n.): late 14c., from Old French rafle "dice game," also "plundering," perhaps from a Germanic source (cf. Middle Dutch raffel "dice game," Old Frisian hreppa "to move," Old Norse hreppa "to reach, get," German raffen "to snatch away, sweep off"), from Proto-Germanic *khrap- "to pluck out, snatch off." The notion would be "to sweep up (the stakes), to snatch (the winnings)." Dietz connects the French word with the Germanic root, but OED is against this. Meaning "sale of chances" first recorded 1766.
raffle (v.): "dispose of by raffle," 1851, from raffle (n.). Related: Raffled; raffling.
rafflesia: genus of Malaysian plants, 1820, named for Sir T. Stamford Raffles (1781-1826), British governor of Sumatra, who introduced it to the West. He reports the native name was petimum sikinlili "Devil's betel-box."
raft (n.1): "floating platform," late 15c., originally "rafter" (early 15c.), from Old Norse raptr "log" (Old Norse -pt- pronounced as -ft-), related to Middle Low German rafter, rachter "rafter" (see rafter).
raft (n.2): "large collection," 1830, variant of raff "heap, large amount," from Middle English raf (cf. raffish, riffraff); form and sense associated with raft (n.1).
rafter (n.): "sloping timber of a roof," Old English ræftras (West Saxon), reftras (Mercian), both plural, related to Old Norse raptr "log" (see raft (n.1)), from Proto-Germanic *raf-.
rag (n.): early 14c., probably from Old Norse rogg "shaggy tuft," earlier raggw-, or possibly from Old Danish rag (see rug), or a back-formation from ragged (c.1300), which is from Old Norse raggaðr "shaggy," via Old English raggig "rag-like." It also may represent an unrecorded Old English cognate of Old Norse rogg. As an insulting term for "newspaper, magazine" it dates from 1734; slang for "tampon, sanitary napkin" is attested from 1930s. Rags "personal clothing" is from 1855, American English. Rags-to-riches "rise from poverty to wealth" is attested by 1896.
rag (v.): "scold," 1739, of unknown origin; perhaps related to Danish dialectal rag "grudge." Related: Ragged; ragging.
rag-bag (n.): 1820, from rag (n.) + bag (n.). Figurative sense of "motley collection" is first recorded 1864.
raga (n.): 1788, from Sanskrit raga-s "harmony, melody, mode in music," literally "color, mood," related to rajyati "it is dyed."
ragamuffin (n.): mid-14c., from Middle English raggi "ragged" + fanciful ending (or else second element is Middle Dutch muffe "mitten"). Ragged was used of the devil from c.1300 in reference to "shaggy" appearance. Used by Langland as the name of a demon (cf. Old French Ragamoffyn, name of a demon in a mystery play); sense of "dirty, disreputable boy" is from 1580s.
rage (n.): c.1300, from Old French raige (11c.), from Medieval Latin rabia, from Latin rabies "madness, rage, fury," related to rabere "be mad, rave." Related to rabies, of which this is the original sense. Similarly, Welsh (cynddaredd) and Breton (kounnar) words for "rage, fury" originally meant "hydrophobia" and are compounds based on the word for "dog" (Welsh ci, plural cwn; Breton ki). The rage "fashion, vogue" dates from 1785.
rage (v.): mid-13c., "to play, romp," from rage (n.). Meaning "be furious" first recorded c.1300. Related: Raged; raging.
ragged (adj.): "rough, shaggy," c.1300, past participle adjective from rag (n.), but earliest use is not directly from the main sense of that word and may reflect a broader, older meaning. Of clothes, early 14c.; of persons, late 14c. Cf. Latin pannosus "ragged, wrinkly," from pannus "piece of cloth."
raggedy (adj.): 1845, U.S. Southern, from ragged + -y (2). Raggedy Ann stories first published 1918, character created by U.S. illustrator Johnny Gruelle (1880–1938). Raggedy-ass by 1930.
raghead (n.): insulting term for "South Asian or Middle Eastern person," 1910, from rag (n.) + head (n.); in reference to turbans, etc.
Ragnarok: in Norse mythology, the last battle of the world, in which gods and men will be destroyed by monsters and darkness, 1770, from Old Norse ragna, genitive of regin "the gods" + rök "destined end" or rökr "twilight."
ragout (n.): 1650s, from French ragoût (mid-17c.), from Middle French ragoûter "awaken the appetite," from Old French re- "back" (see re-) + à "to" + goût "taste," from Latin gustum (nominative gustus); see gusto.
ragtag: 1820, from rag (n.) + tag (n.); originally in expression rag-tag and bobtail "the rabble" (tag-rag and bobtail is found in 1650s), from bobtail "cur," 1610s. Tag and rag was "very common in 16-17th c." [OED]
ragtime (n.): also rag-time, "syncopated, jazzy piano music," 1897, from rag "dance ball" (1895, American English dialect), possibly a shortening of ragged, in reference to the rhythmic imbalance.
If rag-time was called tempo di raga or rague-temps it might win honor more speedily. ... What the derivation of the word is[,] I have not the faintest idea. The negroes call their clog-dancing "ragging" and the dance a "rag." [Rupert Hughes, Boston "Musical Record," April 1900]
ragtop (n.): "convertible car," 1954, from rag (n.) + top (n.1).
ragweed (n.): 1790, from ragged + weed (n.); so called from shape of the leaves. Applied to a different plant, ragwort, from 1650s. Ragwort itself is attested from mid-15c. (see wort).
rah: in cheers, 1870, a shortening of hurrah. Adjective rah-rah is attested from 1907, originally indicating college life generally, later enthusiastic cheerleading.
Rahab: name of a Biblical monster, from Hebrew rahab, literally "storming, against, impetuous," from rahabh "he stormed against" (cf. Arabic rahiba "he feared, was alarmed").
raid (n.): early 15c., "military expedition on horseback," Scottish and northern English form of rade "a riding, journey," from Old English rad "a riding" (see road). The word died out by 17c., but was revived by Scott, 1805 ("The Lay of the Last Minstrel") and 1818 ("Rob Roy"), with extended sense of "attack, foray."
raid (v.): 1864, in a U.S. Civil War context, from raid (n.). Related: Raided; raiding.
raider (n.): 1863, agent noun from raid (v.). A word from the American Civil War.
rail (n.1): "bar," early 14c., from Old French reille, from Vulgar Latin *regla, from Latin regula "straight stick," diminutive form related to regere "to straighten, guide" (see regal). Used figuratively for "thinness" from 1872. Technically, railings (late 15c.) are horizontal, palings are vertical.
rail (n.2): "small bird," mid-15c., from Old French raale (13c.), related to râler "to rattle," of unknown origin, perhaps imitative.
rail (v.): "complain," mid-15c., from Middle French railler "to tease or joke" (15c.), perhaps from Old Provençal ralhar "scoff, to chat, to joke," from Vulgar Latin *ragulare "to bray" (cf. Italian ragghiare "to bray"), from Late Latin ragere "to roar," probably of imitative origin. See rally (v.2). Related: Railed; railing.
raillery (n.): "good-humored ridicule," 1650s, from rail (v.) + -ery, or perhaps from French raillerie, from Middle French railler "to tease."