flotilla (n.) Look up flotilla at Dictionary.com
1711, "a small fleet," from Spanish flotilla, diminutive of flota "float," from flotar "to float," of Germanic origin (see float (v.)).
flotsam (n.) Look up flotsam at Dictionary.com
c.1600, from Anglo-French floteson, from Old French flotaison "a floating," from floter "to float" (of Germanic origin; see float) + -aison, from Latin -ation(em). Spelled flotsen till mid-19c. when it altered, perhaps under influence of many English words in -some.

In British law, flotsam are goods found floating on the sea as a consequence of a shipwreck or action of wind or waves; jetsam are things cast out of a ship in danger of being wrecked, and afterward washed ashore, or things cast ashore by the sailors. Whatever sinks is lagan. Figurative use for "odds and ends" attested by 1861.
flounce (v.) Look up flounce at Dictionary.com
1540s, "to dash, plunge, flop," perhaps from Scandinavian (compare dialectal Swedish flunsa "to plunge," Norwegian flunsa "to hurry," but first record of these is 200 years later than the English word), said to be of imitative origin. Spelling likely influenced by bounce. Notions of "anger, impatience" began to adhere to the word 18c. Related: Flounced; flouncing. As a noun, from 1580s as a motion.
flounce (n.) Look up flounce at Dictionary.com
"wide ruffle," 1713, from Middle English frounce "pleat, wrinkle, fold" (late 14c.), from Old French fronce "line, wrinkle; pucker, crease, fold," from Frankish *hrunkjan "to wrinkle," from Proto-Germanic *hrunk-. Influenced in form by flounce (v.).
flounder (v.) Look up flounder at Dictionary.com
1590s, perhaps an alteration of founder (q.v.), influenced by Dutch flodderen "to flop about," or native verbs in fl- expressing clumsy motion. Figurative use is from 1680s. Related: Floundered; floundering. As a noun derived from this sense, from 1867.
flounder (n.) Look up flounder at Dictionary.com
flatfish, c.1300, from Anglo-French floundre, from Old North French flondre, from Old Norse flydhra; related to Middle Low German vlundere, Danish flynder; ultimately cognate with Greek platys "flat, wide, broad" (see plaice (n.)).
flour (n.) Look up flour at Dictionary.com
early 13c., flur "flower" (see flower (n.)); meaning "finer portion of ground grain" is mid-13c., from the notion of flour as the "finest part" of meal (compare French fleur de farine), as distinguished from the coarser parts (meal). Spelled flower until flour became the accepted form c.1830 to end confusion.
flour (v.) Look up flour at Dictionary.com
"to sprinkle with flour," 1650s, from flour (n.). Related: Floured; flouring.
flourish (v.) Look up flourish at Dictionary.com
c.1300, "to blossom, grow," from Old French floriss-, stem of florir "blossom, flower, bloom, flourish," from Latin florere "to bloom, blossom, flower," figuratively "to flourish, be prosperous," from flos "a flower" (see flora).

Metaphoric sense of "thrive" is mid-14c. Meaning "to brandish (a weapon)" first attested late 14c. Related: Flourished; flourishing.
flourish (n.) Look up flourish at Dictionary.com
c.1500, "a blossom," from flourish (v.). Meaning "ostentatious waving of a weapon" is from 1550s; that of "literary or rhetorical embellishment" is from c.1600.
flout (v.) Look up flout at Dictionary.com
1550s, 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.) Look up flow at Dictionary.com
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 *flo- (cognates: Middle Dutch vloyen, Dutch vloeien "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.) Look up flow at Dictionary.com
mid-15c., "action of flowing," from flow (v.). Meaning "amount that flows" is from 1807. Flow chart attested from 1920.
flower (n.) Look up flower at Dictionary.com
c.1200, from Old French flor "flower, blossom; heyday, prime; fine flour; elite; innocence, virginity" (Modern French fleur), from Latin florem (nominative flos) "flower" (source of Italian fiore, Spanish flor; see flora).

Modern spelling is 14c. Ousted Old English cognate blostm (see blossom (n.)). Also used from 13c. in sense of "finest part or product of anything" and from c.1300 in the sense of "virginity." Flower children "gentle hippies" is from 1967.
flower (v.) Look up flower at Dictionary.com
c.1200, "be vigorous, prosper, thrive," from flower (n.). Of a plant or bud, "to blossom," c.1300. Related: Flowered; flowering.
flowerpot (n.) Look up flowerpot at Dictionary.com
1590s, from flower (n.) + pot (n.1).
flowery (adj.) Look up flowery at Dictionary.com
mid-14c., from flower (n.) + -y (2). Related: Floweriness.
flown Look up flown at Dictionary.com
past participle of fly (v.).
flu (n.) Look up flu at Dictionary.com
1839, flue, shortening of influenza. Spelling flu attested from 1893. For choice of middle syllable, not a common method of shortening in English, Weekley compares tec for detective, scrip for subscription.
flub (v.) Look up flub at Dictionary.com
1924, American English, perhaps suggested by fluff, flop, etc. Related: Flubbed; flubbing. As a noun, by 1952.
fluctuant (adj.) Look up fluctuant at Dictionary.com
1550s, from Latin fluctuantem (nominative fluctuans), present participle of fluctuare "to move in waves" (see fluctuation).
fluctuate (v.) Look up fluctuate at Dictionary.com
1630s, from Latin fluctuatus, past participle of fluctuare "to undulate" (see fluctuation). Related: Fluctuated; fluctuates; fluctuating.
fluctuation (n.) Look up fluctuation at Dictionary.com
mid-15c., from Middle French fluctuation (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 "wave, billow, surge," from past participle of fluere "to flow" (see fluent).
flue (n.) Look up flue at Dictionary.com
"smoke channel in a chimney," 1580s, perhaps related to 15c. word meaning "mouthpiece of a hunting horn," or perhaps from Old English flowan "to flow," and/or Old French fluie "stream."
fluency (n.) Look up fluency at Dictionary.com
1620s, "abundance," later "smooth and easy flow" (1630s), from fluent + -cy. Replaced earlier fluence (c.1600).
fluent (adj.) Look up fluent at Dictionary.com
1580s, "flowing freely" (of water, also of speech), from Latin fluentem (nominative fluens) "lax, relaxed," figuratively "flowing, fluent," present participle of fluere "to flow, stream, run, melt," from PIE *bhleugw-, extended form of *bhleu- "to swell, well up, overflow" (cognates: 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 in Elizabethan times. Related: Fluently.
fluff (n.) Look up fluff at Dictionary.com
"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.) Look up fluff at Dictionary.com
"to shake into a soft mass," 1875, from fluff (n.). Meaning "make a mistake" is from 1884, originally in theater slang. Related: Fluffed; fluffing.
fluffer (n.) Look up fluffer at Dictionary.com
"track sweeper on the London underground," by 1956.
fluffy (adj.) Look up fluffy at Dictionary.com
1825, from fluff + -y (2). Related: Fluffiness.
flugelhorn (n.) Look up flugelhorn at Dictionary.com
1854, from German flügelhorn, from flügel "wing" (related to fliegen "to fly;" see fly (v.1)) + horn "horn" (see horn (n.)).
fluid (adj.) Look up fluid at Dictionary.com
early 15c., from Middle French fluide (14c.) and directly from Latin fluidus "fluid, flowing, moist," from fluere "to flow" (see fluent). Figurative use from 1640s. Related: Fluidly.
fluid (n.) Look up fluid at Dictionary.com
1660s, from fluid (adj.).
fluidity (n.) Look up fluidity at Dictionary.com
c.1600, from French fluidité, from fluide (see fluid (adj.)), or else formed in English from fluid.
fluke (n.1) Look up fluke at Dictionary.com
"flat end of an arm of an anchor," 1560s, perhaps from fluke (n.3) on resemblance of shape, or from Low German flügel "wing." Meaning "whale's tail" (in plural, flukes) is 1725.
fluke (n.2) Look up fluke at Dictionary.com
"lucky stroke, chance hit," 1857, originally a lucky shot at billiards, of uncertain origin.
fluke (n.3) Look up fluke at Dictionary.com
"flatfish," Old English floc "flatfish," related to Old Norse floke "flatfish," flak "disk, floe" (see flake (n.)). The parasite worm (1660s) so called from resemblance of shape.
fluky (adj.) Look up fluky at Dictionary.com
1867, from fluke (n.2) + -y (2).
flume (n.) Look up flume at Dictionary.com
late 12c., "stream," from Old French flum "running water, stream, river," 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.) Look up flummery at Dictionary.com
1620s, a type of coagulated food, from Welsh llymru "sour oatmeal jelly boiled with the husks," of uncertain origin. Figurative use, of flattery, empty talk, is from 1740s.
flummox (v.) Look up flummox at Dictionary.com
1837, cant word, origin uncertain, probably from some forgotten British dialect. Candidates cluster in Herefordshire, Gloucestershire, southern Cheshire and also in Sheffield. "The formation seems to be onomatopœic, expressive of the notion of throwing down roughly and untidily." Never let it be said that the OED editors lacked imagination. Related: Flummoxed.
flung Look up flung at Dictionary.com
past participle of fling (v.).
flunk (v.) Look up flunk at Dictionary.com
1823, American English college slang, original meaning "to back out, give up, fail," traditionally said to be an alteration of British university slang funk "to be frightened, shrink from" (see funk (n.1)). Related: Flunked; flunking.
flunky (n.) Look up flunky at Dictionary.com
also flunkey, 1782, Scottish dialect, "footman, liveried servant," of uncertain origin, perhaps a diminutive variant of flanker. Sense of "flatterer, toady" first recorded 1855.
fluor (n.) Look up fluor at Dictionary.com
16c., and old chemistry term for "minerals which were readily fusible and useful as fluxes in smelting" [Flood], Latin fluor, originally meaning "a flowing, flow" (see fluent). Since 1771 applied to minerals containing fluorine, especially calcium fluoride (fluorspar or fluorite).
fluorescence (n.) Look up fluorescence at Dictionary.com
1852, "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.) Look up fluorescent at Dictionary.com
1853, from fluor- + -escent (see fluorescence). The fluorescent electric lamp patent was applied for in 1896 by U.S. inventor Thomas A. Edison, but such lights were rare before 1938.
fluoridate (v.) Look up fluoridate at Dictionary.com
1949, back-formation from fluoridation. Related: Fluoridated; fluoridating.
fluoridation (n.) Look up fluoridation at Dictionary.com
1904, from fluoride + -ation. In reference to adding traces of fluoride to drinking water as a public health policy, from 1949.
fluoride (n.) Look up fluoride at Dictionary.com
1826, "binary compound of fluorine with another element," from fluorine + -ide.