Online Etymology Dictionary

flue: "smoke channel in a chimney," 1582, perhaps related to 15c. word meaning "mouthpiece of a hunting horn," or perhaps from O.E. flowan "to flow," and/or O.Fr. fluie "stream."
fluent: 1589, from L. fluentem (nom. fluens), prp. of fluere "to flow," from PIE *bhleug- (cf. L. flumen "river;" Gk. phluein "to boil over, bubble up," phlein "to abound"), from *bhleu- "to swell, well up, overthrow," extension of root *bhel- "to blow, swell" (see bole). Used interchangeably with fluid in Elizabethan times.
fluff (n.): 1790, variant of floow "wooly substance, down, nap" (1589), perhaps from Flem. vluwe, from Fr. velu "shaggy, hairy," from L. vellus "fleece," or L. villus "tuft of hair" (see velvet). OED suggests fluff as "an onomatopoeic modification" of floow, "imitating the action of puffing away some light substance." The verb meaning "to shake into a soft mass" is first attested 1885. Slang bit of fluff "young woman" is from 1903.
flugelhorn: 1854, from Ger. flügelhorn, from flügel "wing" + horn "horn."
fluid (adj.): c.1600, from L. fluidus "fluid, flowing," from fluere "to flow" (see fluent). The noun is 1660s, from the adj.
fluke (1): "flat end of an arm of an anchor," 1561, perhaps from fluke (3) on resemblance of shape, or from L.Ger. flügel "wing." Meaning "whale's tail" (in plural) is 1725.
fluke (2): "lucky chance," 1857, originally a lucky shot at billiards, of uncertain origin.
fluke (3): "flatfish," O.E. floc "flatfish," related to O.N. floke "flatfish," flak "disk, floe" (see flake). The parasite worm (1668) so called from resemblance of shape.
flume: c.1175, "stream," from O.Fr. flum, from L. flumen "river," from fluere "to flow" (see fluent). In U.S., used especially of artificial streams channeled for some industrial purpose.
flummox: 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 onomatopoeic, expressive of the notion of throwing down roughly and untidily." Never let it be said that the OED editors lacked imagination.
flunk: 1823, Amer.Eng. 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 (1)).
flunky: 1782, Scottish dial., "footman, liveried servant," of uncertain origin, perhaps a dim. variant of flanker. Sense of "flatterer, toady" first recorded 1855.
fluorescence: 1852, "glowing in ultraviolet light," coined by Eng. mathematician and physicist Sir George G. Stokes (1819-1903) from fluorspar (see fluorine), because in it he first noticed the phenomenon, + ending -escence from opalescence, phosphorescence. The fluorescent electric lamp patent was applied for in 1896 by Thomas A. Edison, but such lights were rare before 1938.
fluoride: 1826, "binary compound of fluorine with another element," from the same source as fluorine (q.v.). Fluoridation, in reference to adding traces of fluorine to drinking water as a public health policy, dates from 1949.
fluorine: 1813, non-metallic element, coined by Eng. chemist Sir Humphry Davy (1778-1829) from fluorspar ("calcium fluoride," modern fluorite), the name of the mineral where it was first found, from L. fluor, originally meaning "a flowing, flow" (see fluent). The mineral name was given by Georg Agricola in 1546, translating Ger. name flusse, so called because it melts easily.
flurry: "snow squall" 1828, Amer.Eng., probably from 17c. flurr "to scatter, fly with a whirring noise," perhaps from M.E. flouren "to sprinkle, as with flour." Sense of "commotion" first recorded 1710.
flush (v.): "fly up suddenly," c.1300, perhaps imitative of the sound of beating wings, or related to flash via its variant flushe. Probably not connected to O.Fr. flux, source of flush (n.). Transitive meaning "to cause to fly, start" is first attested c.1450. The sense of "spurt, rush out suddenly, flow with force" (1548) is probably the same word, with the connecting notion being "sudden movement," but its senses seem more to fit the older ones of flash (now all transferred to this word except in flash flood). The noun sense of "sudden redness in the face" (1630) probably belongs here, too. "A very puzzling word" [Weekley].
flush (adj.): "even, level," c.1550, perhaps from flush (v.) through the notion of a river running full, hence level with its banks. Applied to money since at least c.1600.
flush (n.): "hand of cards all of one suit," 1529, perhaps from M.Fr. flus (15c.), from O.Fr. flux "a flowing," with the sense of "a run" (of cards), from L. fluxus "flux," from fluere "to flow" (see fluent). The form in Eng. probably was influenced by flush (v.).
fluster: 1422 (implied in flostyrynge), from a Scand. source (cf. Icel. flaustr "bustle," flaustra "to bustle"). Originally "to excite," especially with drink; sense of "to flurry, confuse" is from 1724.
flute: late 14c., from O.Fr. flaute, from O.Prov. flaut, of uncertain origin, perhaps imitative or from L. flare "to blow;" perhaps influenced by Prov. laut "lute." The other Germanic words (cf. Ger. flöte) are likewise borrowings from French. Ancient flutes were blown through a mouthpiece, like a recorder; the modern transverse or German flute developed 18c. The modern design and key system of the concert flute were perfected 1834 by Theobald Boehm. The architectural sense of "furrow in a pillar" (1650s) is from fancied resemblance to the inside of a flute split down the middle. Meaning "tall, slender wine glass" is from 1640s. Flutist (c.1600), probably from Fr. flûtiste, replaced M.E. flouter and is preferred in U.S. British preference is flautist (q.v.), a Continental reborrowing that returns the original diphthong.
flutter: O.E. floterian "float to and fro, be tossed by waves," freq. of fleotan "to fleet" (see fleet (n.)).
fluvial: "pertaining to a river," late 14c., from L. fluvialis, from fluvius "river," related to fluere "to flow" (see flow).
flux: late 14c., from O.Fr. flux, from L. fluxus, pp. of fluere "to flow" (see fluent). Originally "excessive flow" (of blood or excrement); an early name for "dysentery;" sense of "continuous succession of changes" is first recorded 1620s.
fly (n.): O.E. fleoge, from P.Gmc. *fleugjon (cf. O.S. fleiga, O.N. fluga, M.Du. vlieghe, Ger. Fliege "fly); lit. "the flying (insect)" (cf. O.E. fleogende "flying"), from same source as fly (v.1). Originally "any winged insect" (hence butterfly, etc.); long used by farmers and gardeners for any insect parasite. Slang adj. meaning "clever, alert, wide awake" first recorded 18c., perhaps from the notion of the insect being hard to catch (other theories, however, trace it to fledge or flash); 1990s use may be a revival or a reinvention. Fly on the wall "unseen observer" first recorded 1949. An O.E. word for "curtain" was fleonet "fly-net." Fly-swatter first attested 1917. Flypaper attested from 1851, though the item itself is said to have become commonly available in London in 1848.
fly (v.1): "to soar through air," O.E. fleogan (class II strong verb; past tense fleag, pp. flogen), from W.Gmc. *fleuganan (cf. O.H.G. fliogan, O.N. flügja, M.Du. vlieghen, Ger. fliegen), from PIE *pleu- "flowing, floating" (cf. Lith. plaukiu "to swim"). The O.E. plural in -n (cf. oxen) gradually normalized 13c.-15c. to -s. Notion of "flapping as a wing does" led to sense of "tent flap" (1810), which yielded (1844) "covering for buttons that close up a garment." Flying buttress is from 1669. Fly-fishing (from fly (n.)) is from 1653; while flying fish is from c.1511. Flying saucer first attested 1947, though the image of saucers for unidentified flying objects is from at least 1880s. Flying Dutchman ghost ship first recorded c.1830, in Jeffrey, Baron de Reigersfeld's "The Life of a Sea Officer." Slang phrase fly off the handle "lose one's cool" dates from 1825. On the fly is 1851. Flying colors (1706) is probably from the image of a naval vessel with the national flag bravely displayed.
fly (v.2): "run away," O.E. fleon (see flee). Fleogan and fleon were often confused in O.E., too. Mod.Eng. distinguishes in preterite: flew/fled.
fly-by-night: 1796, slang, said to be an old term of reproach to a woman signifying that she was a witch; extended 1823 to "anyone who departs hastily from a recent activity," especially while owing money. The two senses involve the two verbs fly.
flyer: "small handbill or fly-sheet," 1889, U.S. slang, from fly (v.1) on notion of "made to be scattered broadcast."
Flynn: surname, from Ir. flann "red."
foal: O.E. fola, from P.Gmc. *fulon (cf. O.H.G. folo, O.N. foli, O.Fris. fola, M.H.G. vole, Ger. Fohlen, Goth. fula), from PIE >*poul-/*pul- "young animal" (cf. Gk. polos "foal," L. pullus "a young animal").
foam (n.): O.E. fam "foam, saliva froth," from W.Gmc. *faima (cf. O.H.G. veim, Ger. Feim), from PIE *poim(n)o- (cf. Skt. phenah; L. pumex "pumice," spuma "foam;" O.C.S. pena "foam;" Lith. spaine "a streak of foam"). The verb is from O.E. famgian "to foam." The rubber or plastic variety so called from 1937.
fob (n.): 1653, "small pocket for valuables," probably related to Low Ger. fobke "pocket," High Ger. fuppe "pocket." Meaning "chain attached to a watch carried in the fob" is from 1885.
fob (v.): "to cheat," 1583, from obsolete noun fobbe "cheat, trickster" (1393), perhaps from O.Fr. forbe "cheat." Alternative etymology holds that the word is perhaps related to Ger. foppen "to jeer at, make a fool of" (see fop); or from Ger. fuppen, einfuppen "to pocket stealthily," which would connect it to fob (n.). To fob (someone) off is first recorded 1597.
foci: plural of focus (q.v.).
focus: 1644, from L. focus "hearth, fireplace," of unknown origin, used in post-classical times for "fire" itself, taken by Kepler (1604) in a mathematical sense for "point of convergence," perhaps on analogy of the burning point of a lens (the purely optical sense of the word may have existed before 1604, but it is not recorded). Introduced into Eng. 1656 by Hobbes. Sense transfer to "center of activity or energy" is first recorded 1796. The verb is first attested 1814 in the literal sense; the fig. sense is recorded earlier (1807).
fodder: O.E. fodor "food," especially "food for cattle," from P.Gmc. *fodran (cf. O.N. foðr, M.Du. voeder, O.H.G. fuotar, Ger. Futter), from PIE *patrom, from *pat- "to feed" (see food).
foe: O.E. gefa "adversary in deadly feud," from fah "at feud, hostile," from P.Gmc. *fakhaz (cf. O.H.G. fehan "to hate," Goth. faih "deception"), probably from PIE base *peik- "evil-minded, treacherous, hostile" (cf. Skt. pisunah "malicious," picacah "demon;" Gk. pikros "bitter;" Lith. piktas "wicked, angry," pekti "to blame"). Weaker sense of "adversary" is first recorded 1607.
fog: 1540s, from Dan. fog "spray, shower, snowdrift," related to O.N. fok "snow flurry." The word meaning "long grass" (c.1300) may be a different word, but the two may connect via a notion of long grass growing in moist dells of northern Europe. Phrase in a fog "at a loss what to do" first recorded c.1600. Foggy Bottom "U.S. Department of State," from the name of a marshy region of Washington, D.C., where many federal buildings are (also with a punning allusion to political murkiness) popularized 1947 by James Reston in "New York Times," but he said it had been used earlier by Edward Folliard of "The Washington Post."
Fogarty: surname, from O.Ir. fogartach "banished."
fogey: "an old, dull fellow," 1780, Scottish foggie, originally "army pensioner or veteran," perhaps connected to fogram (1775) "old-fashioned person;" or from fog in obsolete senses of "moss" or "bloated fat" (1586).
foible: 1648, "weak point of a sword blade" (contrasted to forte), from Fr. foible (adj.) "weak," from O.Fr. foible "feeble," dissimilated from L. flebilis (see feeble). Extended sense of "weak point of character" is first recorded 1673.
foie gras: 1818, short for pâté de foie gras.
foil (v.): c.1300, foilen "to spoil a trace or scent by running over it," from O.Fr. fouler "trample," from V.L. *fullare "to clean cloth" (by treading on it), from L. fullo "one who cleans cloth, fuller," of unknown origin. Sense of "frustrate the efforts of" first recorded 1664.
foil (n.): "thin sheet of metal," late 14c., from O.Fr. fueille "leaf," from L. folia "leaves," pl. (mistaken for fem. sing.) of folium "leaf" (see folio). The sense of "one who enhances another by contrast" (1580s) is from the practice of backing a gem with metal foil to make it shine better. The meaning "light sword used in fencing" (1590s) could be from this sense, or from foil (v.). The modern sense of "metallic food wrap" is from 1946.
foist: 1545, from Du. vuisten "take in hand," from M.Du. vuist "fist." Earliest sense was cheating at dice by concealing one in the palm of the hand; meaning "introduce surreptitiously" is from 1563.
Fokker: Ger. monoplane, 1913, from name of A.H.G. Fokker (1890-1939), Du. engineer and inventor.
fold (v.): O.E. faldan (Mercian), fealdan (W.Saxon), "to bend cloth back over itself," class VII strong verb (past tense feold, pp. fealden), from P.Gmc. *falthanan (cf. O.N. falda, M.L.G. volden, Ger. falten, Goth. falþan), from PIE *pel-to- (cf. Skt. putah "fold, pocket," Alb. pale "fold," M.Ir. alt "a joint"), from base *pel- "to fold." The weak form developed from 15c. Sense of "to yield to pressure" is from late 14c. The noun meaning "a bend or ply in anything" is mid-13c., from the verb. Folder "folding cover for loose papers," is first recorded 1911.
fold (n.): "pen or enclosure for sheep or other domestic animals," O.E. falæd, falud, a Gmc. word (cf. E.Fris. folt "enclosure, dunghill," Dan. fold "pen for sheep"), of uncertain origin.
foliage: 1598, from M.Fr. feuillage, from O.Fr. feuille "leaf" (see foil (n.)). The form altered by infl. of L. folium.