fluorine (n.) Look up fluorine at Dictionary.com
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.
fluoroscopy (n.) Look up fluoroscopy at Dictionary.com
1896, from fluor- (see fluorescence) + -oscopy (see -scope).
flurry (n.) Look up flurry at Dictionary.com
"snow squall" 1828, American English, with earlier senses of "commotion," etc., dating to 1680s; perhaps imitative, or else from 17c. flurr "to scatter, fly with a whirring noise," perhaps from Middle English flouren "to sprinkle, as with flour" (late 14c.).
flurry (v.) Look up flurry at Dictionary.com
1757 in the commotion sense, from flurry (n.); 1883 in the snow sense. Related: Flurried; flurries; flurrying.
flush (v.) Look up flush at Dictionary.com
"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 Old French flux, source of flush (n.).

Transitive meaning "to cause to fly, start" is first attested mid-15c. The sense of "spurt, rush out suddenly, flow with force" (1540s) 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). Meaning "cleanse a drain, etc., with a rush of water" is from 1789. The noun sense of "sudden redness in the face" (1620s) probably belongs here, too. The verb in this sense is from 1660s. "A very puzzling word" [Weekley]. Related: Flushed; flushing.
flush (adj.) Look up flush at Dictionary.com
1550s, "perfect, faultless;" c.1600, "abundant; plentifully supplied (with money, etc.)," perhaps from flush (v.) through the notion of a river running full, hence level with its banks. Meaning "even, level" is from 1620s.
flush (n.) Look up flush at Dictionary.com
"hand of cards all of one suit," 1520s, perhaps from Middle French flus (15c.), from Old French flux "a flowing," with the sense of "a run" (of cards), from Latin fluxus "flux," from fluere "to flow" (see fluent). The form in English probably was influenced by flush (v.).
Flushing Look up Flushing at Dictionary.com
New York village established 1645 by English Puritans (now a neighborhood in Queens), an English corruption of Dutch Vlissingen, name of Dutch town where the Puritans had taken refuge, literally "flowing" (so called for its location on an estuary of the West Scheldt), related to flush (v.).
fluster (v.) Look up fluster at Dictionary.com
early 15c. (implied in flostyrynge), from a Scandinavian source (compare Icelandic flaustr "bustle," flaustra "to bustle"). Originally "to excite," especially with drink; sense of "to flurry, confuse" is from 1724. Related: Flustered; flustering. As a noun, 1710, from the verb.
flustrated (adj.) Look up flustrated at Dictionary.com
1712, jocular formation from fluster + frustrated.
flute (n.) Look up flute at Dictionary.com
early 14c., from Old French flaute (12c.), from Old Provençal flaut, of uncertain origin, perhaps imitative or from Latin flare "to blow;" perhaps influenced by Provençal laut "lute." The other Germanic words (such as German 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 older style then sometimes were called flûte-a-bec (French, literally "flute with a beak"). 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.
flute (v.) Look up flute at Dictionary.com
late 14c., "to play upon the flute," from flute (n.). Meaning "to make (architectural) flutes" is from 1570s. Related: Fluted; fluting.
fluted (adj.) Look up fluted at Dictionary.com
1610s, past participle adjective from flute (v.).
flutist (n.) Look up flutist at Dictionary.com
c.1600, probably from French flûtiste; replaced Middle English flouter (early 13c., from Old French flauteor) and is preferred in U.S. The British preference is flautist (q.v.), a Continental reborrowing that returns the original diphthong.
flutter (v.) Look up flutter at Dictionary.com
Old English floterian "to flutter, fly, flicker, float to and fro, be tossed by waves," frequentative of flotian "to float" (see float (v.)). Related: Fluttered; fluttering. As a noun from 1640s; meaning "state of excitement" is 1740s.
fluvial (adj.) Look up fluvial at Dictionary.com
"pertaining to a river," late 14c., from Latin fluvialis "of a river," from fluvius "river," related to fluere "to flow" (see flow (v.)).
flux (n.) Look up flux at Dictionary.com
late 14c., from Old French flus "flowing, rolling, bleeding," or directly from Latin fluxus "flowing, loose, slack," past participle 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. The verb is early 15c., from the noun.
fly (n.) Look up fly at Dictionary.com
Old English fleoge "fly, winged insect," from Proto-Germanic *fleugjon (cognates: Old Saxon fleiga, Old Norse fluga, Middle Dutch vlieghe, Dutch vlieg, Old High German flioga, German Fliege "fly); literally "the flying (insect)" (compare Old English 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. The Old English plural in -n (as in oxen) gradually normalized 13c.-15c. to -s. Fly on the wall "unseen observer" first recorded 1881. An Old English word for "curtain" was fleonet "fly-net." Fly-swatter as a bit of wire mesh on a handle first attested 1917. Fly-fishing is from 1650s.

From the verb and the notion of "flapping as a wing does" comes the noun sense of "tent flap" (1810), which yielded "covering for buttons that close up a garment" (1844). The sense of "a flight, flying" is from mid-15c. Baseball fly ball attested by 1866. To do something on the fly is 1856, apparently from baseball.
When the catcher sees several fielders running to catch a ball, he should name the one he thinks surest to take it, when the others should not strive to catch the ball on the fly, but only, in case of its being missed, take it on the bound. ["The American Boys Book of Sports and Games," New York, 1864]
fly (v.1) Look up fly at Dictionary.com
"to soar through air," Old English fleogan "to fly" (class II strong verb; past tense fleag, past participle flogen), from Proto-Germanic *fleugan "to fly" (cognates: Old Saxon and Old High German fliogan, Old Norse flügja, Old Frisian fliaga, Middle Dutch vlieghen, Dutch vliegen, German fliegen), from PIE *pleu- "flowing, floating" (see pluvial). Related: Flew; flied (baseball); flying. Slang phrase fly off the handle "lose one's cool" dates from 1825.
fly (v.2) Look up fly at Dictionary.com
"run away," Old English fleon (see flee). Fleogan and fleon were often confused in Old English, too. Modern English distinguishes in preterite: flew/fled.
fly (adj.) Look up fly at Dictionary.com
slang, "clever, alert, wide awake," late 18c., perhaps from fly (n.) on the notion of the insect being hard to catch. Other theories, however, trace it to fledge or flash. Slang use in 1990s might be a revival or a reinvention.
fly-by-night (n.) Look up fly-by-night at Dictionary.com
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.
fly-over (n.) Look up fly-over at Dictionary.com
also flyover, 1901 of bridges, 1931, of aircraft flights, from fly (v.1) + over (adv.).
flyer (n.) Look up flyer at Dictionary.com
also flier, mid-15c., "something that flies," agent noun of fly (v.1). Meaning "something that goes fast" is from 1795; that of "aviator" is from 1934. Meaning "speculative investment" is from 1846 (on the notion of a "flying leap"). Meaning "small handbill or fly-sheet" is from 1889, U.S. slang (originally especially of police bulletins), on notion of "made to be scattered broadcast." Meaning "aviator" is from World War I. Related: Fliers; flyers.
flying (adj.) Look up flying at Dictionary.com
Old English fleogende "flying, winged," present participle of fly (v.1). Flying buttress is from 1660s; flying fish is from 1510s. Flying saucer first attested 1947, though the image of saucers for unidentified flying objects is from at least 1880s. Flying Dutchman, ghost ship off the Cape of Good Hope, attested since 1803 [John Leyden, "Scenes of Infancy," who describes it as "a common superstition of mariners"]. Flying colors (1706) probably is from the image of a naval vessel with the national flag bravely displayed.
Flynn Look up Flynn at Dictionary.com
surname, from Irish flann "red."
flypaper (n.) Look up flypaper at Dictionary.com
1851 (though the item itself is said to have become commonly available in London in 1848), from fly (n.1) + paper (n.).
flyte (v.) Look up flyte at Dictionary.com
Old English flitan "to contend, struggle, quarrel;" related to German fleiß, Dutch vlijt "diligence, industry."
flyway (n.) Look up flyway at Dictionary.com
1891, originally of bird migration paths, from fly (v.1) + way (n.).
flywheel (n.) Look up flywheel at Dictionary.com
1784, from fly (n.) "speed-regulating device" (from fly (v.1)) + wheel (n.).
fo'c'sle (n.) Look up fo'c'sle at Dictionary.com
see forecastle.
foal (n.) Look up foal at Dictionary.com
Old English fola "foal, colt," from Proto-Germanic *fulon (cognates: Old Saxon folo, Middle Dutch and Dutch veulen, Old Norse foli, Old Frisian fola, Old High German folo, German Fohlen, Gothic fula), from PIE *pulo- "young of an animal" (cognates: Greek polos "foal," Latin pullus "a young animal," Albanian pele "mare"), from root *pau- "few, little" (see few).
foal (v.) Look up foal at Dictionary.com
"give birth (to a foal)," late 14c., from foal (n.). Related: Foaled; foaling.
foam (n.) Look up foam at Dictionary.com
Old English fam "foam, saliva froth," from West Germanic *faimo- (cognates: Old High German veim, German Feim), from PIE *(s)poi-mo-, a root with connotations of "foam, froth" (cognates: Sanskrit phenah; Latin pumex "pumice," spuma "foam;" Old Church Slavonic pena "foam;" Lithuanian spaine "a streak of foam"). The rubber or plastic variety so called from 1937.
foam (v.) Look up foam at Dictionary.com
Old English famgian "to foam," from the source of foam (n.). Related: Foamed; foaming.
foamy (adj.) Look up foamy at Dictionary.com
Old English faemig; see foam (n.) + -y (2). Related: Foaminess.
fob (n.) Look up fob at Dictionary.com
1650s, "small pocket for valuables," probably related to Low German fobke "pocket," High German fuppe "pocket," "a dialectal word used in Livonia" [Klein]. Meaning "chain attached to a watch carried in the fob" is from 1885.
fob (v.) Look up fob at Dictionary.com
"to cheat," late 14c., from obsolete noun fobbe "cheat, trickster" (late 14c.), perhaps from Old French forbe "cheat" [OED]. Alternative etymology holds that the word is perhaps related to German foppen "to jeer at, make a fool of" (see fop); or from German fuppen, einfuppen "to pocket stealthily," which would connect it to fob (n.). To fob (someone) off is first recorded 1590s. Related: Fobbed; fobbing.
focal (adj.) Look up focal at Dictionary.com
1690s, from Modern Latin focalis; see focus (n.) + -al (1).
foci (n.) Look up foci at Dictionary.com
plural of focus (n.).
focus (n.) Look up focus at Dictionary.com
1640s, from Latin focus "hearth, fireplace" (also, figuratively, "home, family"), 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 Kepler, but it is not recorded). Introduced into English 1650s by Hobbes. Sense transfer to "center of activity or energy" is first recorded 1796.
focus (v.) Look up focus at Dictionary.com
1775 in the literal sense; 1807 in the figurative sense, from focus (n.). Related: Focused; focusing; less commonly focussed; focussing.
fodder (n.) Look up fodder at Dictionary.com
Old English fodder "food," especially "food for cattle," from Proto-Germanic *fodran (cognates: Old Norse foðr, Middle Dutch voeder, Old High German fuotar, German Futter), from PIE *patrom, from *pa- "to feed" (see food).
foe (n.) Look up foe at Dictionary.com
Old English gefa "foe, enemy, adversary in a blood feud" (the prefix denotes "mutuality"), from fah "at feud, hostile," from Proto-Germanic *fakhaz (cognates: Old High German fehan "to hate," Gothic faih "deception"), probably from PIE root *peig- (2) "evil-minded, treacherous, hostile" (cognates: Sanskrit pisunah "malicious," picacah "demon;" Greek pikros "bitter;" Latin piget "it irks, troubles, displeases," piger "reluctant, lazy;" Lithuanian piktas "wicked, angry," pekti "to blame"). Weaker sense of "adversary" is first recorded c.1600.
foetal (adj.) Look up foetal at Dictionary.com
see fetal; for spelling, see oe.
foetid (adj.) Look up foetid at Dictionary.com
see fetid; for spelling, see oe.
foetus (n.) Look up foetus at Dictionary.com
see fetus; for spelling, see oe.
fog (v.) Look up fog at Dictionary.com
1590s, from fog (n.1). Related: Fogged; fogging.
fog (n.1) Look up fog at Dictionary.com
"thick, obscuring mist," 1540s, probably from a Scandinavian source akin to Danish fog "spray, shower, snowdrift," Old Norse fok "snow flurry," fjuk "snow storm." Compare also Old English fuht, Dutch vocht, German Feucht "moist." Figurative phrase in a fog "at a loss what to do" first recorded c.1600.
fog (n.2) Look up fog at Dictionary.com
"long grass," c.1300, probably of Scandinavian origin; compare Norwegian fogg "long grass in a moist hollow," Icelandic fuki "rotten sea grass." The connection to fog (n.1), via a notion of long grass growing in moist dells of northern Europe, is tempting but not proven. Watkins suggests derivation from PIE *pu- "to rot, decay."