racket (n.1) Look up racket at Dictionary.com
"loud noise," 1560s, perhaps imitative. Klein compares Gaelic racaid "noise." Meaning "dishonest activity" (1785) is perhaps from racquet, via notion of "game," reinforced by rack-rent "extortionate rent" (1590s), from rack (n.1). But it might as well be an extended sense of "loud noise" by way of "noise or disturbance made to distract a pick-pocket's victim."
racket (n.2) Look up racket at Dictionary.com
"handled paddle or netted bat used in tennis, etc.;" see racquet.
racketeer Look up racketeer at Dictionary.com
1928 (noun and verb), from racket (n.1) + -eer. Related: Racketeering (1928).
raconteur (n.) Look up raconteur at Dictionary.com
"storyteller, person skilled in relating anecdotes," 1828, from French raconteur, from raconter "to recount, tell, narrate," from re- (see re-) + Old French aconter "to count, render account" (see account (v.); and compare recount (v.1)). Related: Raconteuse (fem.).
racquet (n.) Look up racquet at Dictionary.com
"handled hitting device used in tennis, etc.," c.1500, probably originally "tennis-like game played with open hand" (late 14c.), from Middle French rachette, requette (Modern French raquette) "racket for hitting; palm of the hand," perhaps via Italian racchetta or Spanish raqueta, both often said to be from Arabic rahat, a form of raha "palm of the hand," but this has been doubted. Compare French jeu de paume "tennis," literally "play with the palm of the hand," and compare tennis).
racquetball (n.) Look up racquetball at Dictionary.com
1972, from racquet + ball (n.1).
racy (adj.) Look up racy at Dictionary.com
1650s, "having a characteristic taste" (of wines, fruits, etc.), from race (n.2) in its older sense of "flavor" or in the sense "class of wines" + -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). Related: Racily; raciness.
rad Look up rad at Dictionary.com
"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 (adj.)).
radar (n.) Look up radar at Dictionary.com
"electronic system for locating objects by means of radio waves," 1941, acronym (more or less) from radio detecting and ranging. The U.S. choice, it won out over British radiolocation. Figurative from 1950.
radial (adj.) Look up radial at Dictionary.com
c.1400, "of or like a ray or radius," from Medieval Latin radialis, from Latin radius "shaft, rod; spoke of a wheel; beam of light" (see radius). As a noun, a type of tire, attested from 1965, short for radial-ply (tire). Related: Radially.
radian (n.) Look up radian at Dictionary.com
"angle subtended at the center of a circle by an arc equal in length to the radius," 1879, from radius.
radiance (n.) Look up radiance at Dictionary.com
c.1600, "brilliant light," from radiant or else from Medieval Latin radiantia "brightness," from radiare "to beam, shine" (see radiation). Figurative use from 1761. Related: Radiancy.
radiant (adj.) Look up radiant at Dictionary.com
mid-15c., from Middle French radiant and directly from Latin radiantem (nominative radians) "beaming, shining," present participle of radiare "to beam, shine" (see radiation). Of beauty, etc., first attested c.1500. Related: Radiantly.
radiant (n.) Look up radiant at Dictionary.com
"point or object from which light radiates," 1727; see radiant (adj.). In astronomy, of meteor showers, from 1864.
radiate (v.) Look up radiate at Dictionary.com
1610s, "spread in all directions from a point," from Latin radiatus, past participle of radiare "to beam, shine, gleam; make beaming" (see radiation). Meaning "be radiant, give off rays (of light or heat)" is from 1704. Related: Radiated; radiates; radiating.
radiate (adj.) Look up radiate at Dictionary.com
"having rays, furnished with rays, shining," 1660s, from Latin radiatus (see radiate (v.)).
radiation (n.) Look up radiation at Dictionary.com
mid-15c., "act or process of radiating," from Middle French radiation and directly from Latin radiationem (nominative radiatio) "a shining, radiation," noun of action from past participle stem of radiare "to beam, shine, gleam; make beaming," from radius "beam of light; spoke of a wheel" (see radius). Meaning "rays or beams emitted" is from 1560s. Meaning "divergence from a center" is 1650s.
radiative (adj.) Look up radiative at Dictionary.com
"having a tendency to radiate," 1820, from radiate (v.) + -ive. Related: Radiativity.
radiator (n.) Look up radiator at Dictionary.com
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.) Look up radical at Dictionary.com
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. Radical sign in mathematics is from 1680s.

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 empiricism coined 1897 by William James (see empiricism).
radical (n.) Look up radical at Dictionary.com
1630s, "root part of a word, from radical (adj.) Political sense from 1802; chemical sense from 1816.
radicalism (n.) Look up radicalism at Dictionary.com
1819 in the political sense, from radical (adj.) + -ism.
radicality (n.) Look up radicality at Dictionary.com
1640s, from radical (adj.) + -ity.
radicalize (v.) Look up radicalize at Dictionary.com
1820, from radical (adj.) + -ize. Related: Radicalized; radicalizing.
radically (adv.) Look up radically at Dictionary.com
c.1600, "thoroughly;" 1620s with reference to roots and origins, from radical (adj.) + -ly (2).
radicand (n.) Look up radicand at Dictionary.com
the number under a radical sign, from Latin radicandus, gerundive of radicare (see radicant).
radicant (adj.) Look up radicant at Dictionary.com
"bringing forth roots," 1735, from Latin radicantem (nominative radicans), present participle of radicare, from radix "root" (see radish).
radicle (n.) Look up radicle at Dictionary.com
1670s, in botany, from Latin radicula, diminutive of radix (see radish).
radicular (adj.) Look up radicular at Dictionary.com
"pertaining to roots," 1830, from Modern Latin radicula, diminutive of Latin radix (see radish) + -ar.
radio (n.) Look up radio at Dictionary.com
"wireless transmission of voice signals with radio waves," 1907, abstracted from earlier combinations such as radio-receiver (1903), radiophone (1881), radio-telegraphy (1898), from radio- as a comb. form of Latin radius "beam." Use for "radio receiver" is first attested 1913; sense of "sound broadcasting as a medium" is from 1913.
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]
In U.S., stations were broadcasting news and music by late 1920, but the new medium caught on nationwide as a fad in the winter of 1921-22; as late as July 1921 the "New York Times" had called it wireless telephony, and wireless remained more widespread until World War II, when military preference for radio turned the tables. As an adjective by 1912, "by radio transmission;" meaning "controlled by radio" from 1974. Radio _______ "radio station or service from _______" is recorded from 1920. A radio shack (1946) was a small building housing radio equipment.
radio (v.) Look up radio at Dictionary.com
1916, from radio (n.). Related: Radioed; radioing.
radio- Look up radio- at Dictionary.com
word-forming element meaning 1. "ray, ray-like" (see radius); 2. "radial, radially" (see radial (adj.)); 3. "by means of radiant energy" (see radiate (v.)); 4. "radioactive" (see radioactive); 5. "by radio" (see radio (n.)).
radio-carbon (n.) Look up radio-carbon at Dictionary.com
"Carbon-14," 1940, from radio-, comb. form of radioactive, + carbon. Radio-carbon dating is attested from 1949.
radio-telephone (n.) Look up radio-telephone at Dictionary.com
1900, from radio (n.) + telephone (n.).
radioactive (adj.) Look up radioactive at Dictionary.com
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.) Look up radioactivity at Dictionary.com
1899, from French radioactivité, coined 1898 by the Curies; see radioactive.
radiocast (n.) Look up radiocast at Dictionary.com
1924, from radio (n.) + ending from broadcast.
radiography (n.) Look up radiography at Dictionary.com
1896, from radiograph (1880), originally a device to measure sunshine; from radio-, comb. form of radiation, + -graph. As a type of image-making device, from 1896.
radioisotope (n.) Look up radioisotope at Dictionary.com
1946, from radio-, comb. form of radiation, + isotope.
radiolarian (n.) Look up radiolarian at Dictionary.com
1862, from Radiolaria, Modern Latin classification name, from Latin radiolus, diminutive of radius (q.v.).
radiology (n.) Look up radiology at Dictionary.com
1900, "medical use of X-rays," later extended to "scientific study of radiation," from radio-, comb. form of radiation, + Greek-based scientific suffix -ology. Related: Radiological.
radiometric (adj.) Look up radiometric at Dictionary.com
1877, from radiometer "instrument to transform radiant energy into mechanical work" (1875), radiometry, from radio-, here indicating "radiant energy," + -metric. Radiometric dating attested from 1906.
radioscopy (n.) Look up radioscopy at Dictionary.com
1896, from radio- + -scopy.
radiotherapy (n.) Look up radiotherapy at Dictionary.com
1903, from radio- + therapy.
radish (n.) Look up radish at Dictionary.com
late Old English rædic "radish," from Latin radicem (nominative radix) "root, radish," from PIE root *wrad- "twig, root" (cognates: Greek rhiza, Lesbian brisda "root;" Greek hradamnos "branch;" Gothic waurts, Old English wyrt; Welsh gwridd, Old Irish fren "root"). Spelling perhaps influenced by Old French radise, variant of radice, from Vulgar Latin *radicina, from radicem.
radium (n.) Look up radium at Dictionary.com
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.) Look up radius at Dictionary.com
1590s, "cross-shaft," from Latin radius "staff, stake, rod; spoke of a wheel; ray of light, beam of light; radius of a circle," 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 (the Latin word had been used thus by the Romans).
Radnor Look up Radnor at Dictionary.com
place in eastern Wales, the name is Old English, literally "at the red bank," from Old English read (dative singular readan; see red (n.1) + ofer "bank, slope."
radon (n.) Look up radon at Dictionary.com
heaviest gaseous element, 1918, from German Radon, 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.) Look up radula at Dictionary.com
surgical instrument, 1753, from Latin radula "scraper, scraping iron," from radere "to scrape" (see raze). Related: Radular.