Online Etymology Dictionary

flourish (n.): c. 1500, "a blossom," from flourish (v.). Meaning "an ostentatious waving of a weapon" is from 1550s; that of "excessive literary or rhetorical embellishment" is from c. 1600; in reference to decorative curves in penmanship, 1650s; as "a fanfare of trumpets," 1590s.
flourishing (adj.): late 14c., "prospering, thriving;" c. 1400, "full of flowers," present participle adjective from flourish (v.). Related: Flourishingly.
flout (v.): "treat with disdain or contempt" (transitive), 1550s, intransitive sense "mock, jeer, scoff" is from 1570s; of uncertain origin; perhaps a special use of Middle English flowten "to play the flute" (compare Middle Dutch fluyten "to play the flute," also "to jeer"). Related: Flouted; flouting.
flow (v.): Old English flowan "to flow, stream, issue; become liquid, melt; abound, overflow" (class VII strong verb; past tense fleow, past participle flowen), from Proto-Germanic *flowan "to flow" (source also of Middle Dutch vloyen, Dutch vloeien, vloeijen "to flow," Old Norse floa "to deluge," Old High German flouwen "to rinse, wash"), probably from PIE *pleu- "flow, float" (see pluvial). The weak form predominated from 14c., but strong past participle flown is occasionally attested through 18c. Related: Flowed; flowing.
flow (n.): mid-15c., "action of flowing," from flow (v.). Meaning "amount that flows" is from 1807. Sense of "any strong, progressive movement comparable to the flow of a river" is from 1640s. Flow chart attested from 1920 (flow-sheet in same sense from 1912). To go with the flow is by 1977, apparently originally in skiing jargon.
Go with the flow, enjoy the forces, let ankles, knees, hips and waist move subtly to soak up potential disturbances of acceleration and deceleration. ["Ski" magazine, November 1980]
flower (n.): c. 1200, flour, also flur, flor, floer, floyer, flowre, "the blossom of a plant; a flowering plant," from Old French flor "flower, blossom; heyday, prime; fine flour; elite; innocence, virginity" (12c., Modern French fleur), from Latin florem (nominative flos) "flower" (source of Italian fiore, Spanish flor; compare flora).

From late 14c. in English as "blossoming time," also, figuratively, "prime of life, height of one's glory or prosperity, state of anything that may be likened to the flowering state of a plant." As "the best, the most excellent; the best of its class or kind; embodiment of an ideal," early 13c. (of persons, mid-13c. of things); for example flour of milk "cream" (early 14c.); especially "wheat meal after bran and other coarse elements have been removed, the best part of wheat" (mid-13c.). Modern spelling and full differentiation from flour (n.) is from late 14c.

In the "blossom of a plant" sense it ousted its Old English cognate blostm (see blossom (n.)). Also used from Middle English as a symbol of transitoriness (early 14c.); "a beautiful woman" (c. 1300); "virginity" (early 14c.). Flower-box is from 1818. Flower-arrangement is from 1873. Flower child "gentle hippie" is from 1967.
flower (v.): c. 1200, "be vigorous, prosper, thrive," from flower (n.). Of a plant or bud, "to blossom," c. 1300. Meaning "adorn or cover with flowers" is from 1570s. Related: Flowered; flowering.
flower-pot (n.): also flowerpot, 1590s, from flower (n.) + pot (n.1).
flowery (adj.): mid-14c., from flower (n.) + -y (2). Figurative sense "richly embellished," in reference to language, is from c. 1600. Related: Floweriness.
flown: past participle of fly (v.), from Middle English flogen, flowen. Also formerly the past participle of flow (v.).
Floyd: masc. proper name, variant of Lloyd.
flu (n.): 1839, flue, shortening of influenza. Spelling flu attested from 1893. The abstraction of the middle syllable is an uncommon method of shortening words in English; Weekley compares tec for detective, scrip for subscription.
flub (v.): "botch, bungle," 1924, American English, of uncertain origin, perhaps suggested by fluff, flop, etc. Related: Flubbed; flubbing. As a noun, by 1952.
fluctuant (adj.): "moving like a wave," 1550s, from Latin fluctuantem (nominative fluctuans), present participle of fluctuare "to move in waves" (see fluctuation).
fluctuate (v.): 1630s, from Latin fluctuatus, past participle of fluctuare "to undulate" (see fluctuation). Related: Fluctuated; fluctuates; fluctuating.
fluctuation (n.): mid-15c., from Old French fluctuacion (12c.) or directly from Latin fluctuationem (nominative fluctuatio) "a wavering, vacillation," noun of action from past participle stem of fluctuare "to undulate, to move in waves," from fluctus "a wave, billow, surge, a flowing," from past participle of fluere "to flow" (see fluent).
flue (n.): "smoke channel in a chimney," 1580s, of uncertain origin, perhaps related to Middle English flue, flewe "mouthpiece of a hunting horn" (early 15c.), which is perhaps from Old French fluie "stream;" or the modern word is perhaps from Old English flowan "to flow." Originally a small chimney in a furnace connected to the main chimney.
fluency (n.): 1620s, "abundance;" 1630s, "smooth and easy flow," from fluent + -cy. Replaced earlier fluence (c. 1600).
fluent (adj.): 1580s, "flowing freely" (of water), also, of speakers, "able and nimble in the use of words," from Latin fluentem (nominative fluens) "lax, relaxed," figuratively "flowing, fluent," present participle of fluere "to flow, stream, run, melt," from extended form of PIE root *bhleu- "to swell, well up, overflow" (source also of Latin flumen "river;" Greek phluein "to boil over, bubble up," phlein "to abound"), an extension of root *bhel- (2) "to blow, inflate, swell;" see bole. Used interchangeably with fluid (adj.) in 17c. in the sense "changeable, not rigid." Related: Fluently.
fluff (n.): "light, feathery stuff," 1790, apparently a variant of floow "wooly substance, down, nap" (1580s), perhaps from Flemish vluwe, from French velu "shaggy, hairy," from Latin vellus "fleece," or Latin villus "tuft of hair" (see velvet). OED suggests fluff as "an imitative modification" of floow, "imitating the action of puffing away some light substance." Slang bit of fluff "young woman" is from 1903. The marshmallow confection Fluff dates to c. 1920 in Massachusetts, U.S.
fluff (v.): "to shake into a soft mass," 1875, from fluff (n.). Meaning "make a mistake" is from 1884, originally in theater slang. Related: Fluffed; fluffing.
fluffy (adj.): "containing or resembling fluff," 1825, from fluff (n.) + -y (2). Related: Fluffiness.
flugelhorn (n.): 1854, from German flügelhorn, from flügel "wing" (related to fliegen "to fly;" see fly (v.1)) + horn "horn" (see horn (n.)).
fluid (adj.): early 15c., "liquid, capable of flowing," from Middle French fluide (14c.) and directly from Latin fluidus "fluid, flowing, moist," from fluere "to flow" (see fluent). Figurative use, of non-material things, "not fixed or rigid," from 1640s. Related: Fluidly.
fluid (n.): "substance capable of flowing," 1660s, from fluid (adj.). Related: Fluidal (1869), fluidic (1821, Marmaduke Tulket).
fluidity (n.): c. 1600, from French fluidité, from fluide (see fluid (adj.)), or else formed in English from fluid.
fluke (n.1): "flat end of an arm of an anchor," 1560s, perhaps from fluke (n.3) on resemblance of shape, or from Low German flügel "wing." Transferred meaning "whale's tail" (in plural, flukes) is by 1725, so called from resemblance.
fluke (n.2): "lucky stroke, chance hit," 1857, also flook, said to be originally a lucky shot at billiards, of uncertain origin. Century Dictionary connects it with fluke (n.1) in reference to the whale's use of flukes to get along rapidly (to go a-fluking or some variant of it, "go very fast," is in Dana, Smyth, and other sailors' books of the era). OED (2nd ed. print) allows only that it is "Possibly of Eng. dialectal origin."
fluke (n.3): "flatfish," Old English floc "flatfish," related to Old Norse floke "flatfish," flak "disk, floe," from Proto-Germanic *flok-, from PIE root *plak- (1) "to be flat" (see placenta). The parasite worm (1660s) so called from resemblance of shape.
fluky (adj.): "depending on chance rather than skill," 1867, from fluke (n.2) + -y (2).
flume (n.): late 12c., "stream," from Old French flum "running water, stream, river; dysentery," from Latin flumen "flood, stream, running water," from fluere "to flow" (see fluent). In U.S., used especially of artificial streams channeled for some industrial purpose.
flummery (n.): 1620s, a type of coagulated food, from Welsh llymru "sour oatmeal jelly boiled with the husks," of uncertain origin. Later of a sweet dish in cookery (1747). Figurative use, of flattery, empty talk, is from 1740s.
flummox (v.): 1837, cant word, also flummux, of uncertain origin, probably risen out of a British dialect (OED finds candidate words in Herefordshire, Gloucestershire, southern Cheshire, and Sheffield). "The formation seems to be onomatopœic, expressive of the notion of throwing down roughly and untidily" [OED]. Related: Flummoxed; flummoxing.
flung: past participle of fling (v.).
flunk (v.): 1823, American English college slang, original meaning "to back out, give up, fail," of obscure origin, traditionally said to be an alteration of British university slang funk "to be frightened, shrink from" (see funk (n.1)). Meaning "cause to fail, give a failing mark to" is from 1843. Related: Flunked; flunking.
flunky (n.): also flunkey, 1782, Scottish dialect, "footman, liveried servant," of uncertain origin, perhaps a diminutive variant of flanker (in reference to servants running alongside coaches; compare footman). Sense of "flatterer, toady" first recorded 1855. "Recent in literature, but prob. much older in colloquial speech" [Century Dictionary].
fluonomist (n.): said to be a humorous title for a chimney-sweep, 1947 according to OED, from flue + ending from economist, etc.
fluor (n.): 1660s, an old chemistry term for "minerals which were readily fusible and useful as fluxes in smelting" [Flood], from Latin fluor, originally meaning "a flowing, flow" (see fluent), said to be from a translation of the German miners' name, flusse. Since 1771 applied to minerals containing fluorine, especially calcium fluoride (fluorspar or fluorite).
fluoresce (v.): 1866 (implied in fluoresced), back-formation from fluorescence. Related: Fluorescing.
fluorescence (n.): 1852, "property of glowing in ultraviolet light," coined by English mathematician and physicist Sir George G. Stokes (1819-1903) from fluorspar (see fluorine), because in it he first noticed the phenomenon, + -escence, on analogy of phosphorescence.
fluorescent (adj.): 1853 (Stokes), from fluor- (see fluoro-) + -escent (see fluorescence). The electric fluorescent lamp was invented by Edison in 1896, but such lights were rare in homes before improved bulbs became available in the mid-1930s.
fluoridate (v.): 1949, back-formation from fluoridation. Related: Fluoridated; fluoridating.
fluoridation (n.): 1904, "process of absorbing fluoride," from fluoride + -ation. In reference to adding traces of fluoride to drinking water as a public health policy, from 1949.
fluoride (n.): "compound of fluorine with another element," 1826, from fluorine + -ide.
fluorine (n.): non-metallic element, 1813, coined by English chemist Sir Humphry Davy (1778-1829) from fluorspar ("calcium fluoride," modern fluorite), the late 18c. name of the mineral where it was first found (see fluor) + chemical suffix -ine (2). Not isolated until 1886. Related: Fluorinate; fluorination.
fluoro-: before vowels fluor-, comb. form of fluorine.
fluorocarbon (n.): 1937, from fluoro- + carbon.
fluoroscopy (n.): 1896, from fluoroscope (1896) "device for observing x-rays by means of action in fluorescent substances," from fluoro- + -scope. Related: Fluoroscopic.
flurry (n.): "snow squall" 1828, American English; earlier with a sense of "commotion, state of perturbed action" (1710), "a gust, a squall" (1690s); perhaps imitative, or else from 17c. flurr "to scatter, fly with a whirring noise," which is perhaps from Middle English flouren "to sprinkle, as with flour" (late 14c.).
flurry (v.): 1757, "produce agitation of feeling in, confuse by excitement," from flurry (n.). From 1883 of snow. Related: Flurried; flurries; flurrying.