fluoride (n.) Look up fluoride at Dictionary.com
"compound of fluorine with another element," 1826, from fluorine + -ide.
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. Related: Fluorinate; fluorination.
fluoro- Look up fluoro- at Dictionary.com
before vowels fluor-, comb. form of fluorine.
fluorocarbon (n.) Look up fluorocarbon at Dictionary.com
1937, from fluoro- + carbon.
fluoroscopy (n.) Look up fluoroscopy at Dictionary.com
1896, from fluoroscope (1896) "device for observing x-rays by means of action in fluorescent substances," from fluoro- + -scope. Related: Fluoroscopic.
flurry (n.) Look up flurry at Dictionary.com
"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.) Look up flurry at Dictionary.com
1757, "produce agitation of feeling in, confuse by excitement," from flurry (n.). From 1883 of snow. Related: Flurried; flurries; flurrying.
flush (v.1) Look up flush at Dictionary.com
mid-13c., flusshen "move rapidly or violently; rush, dart, spring" (intransitive); late 15c., flush up, transitive, "cause to fly; start or flush (birds)," perhaps imitative of the sound of beating wings.

The sense of "spurt, rush out suddenly, flow with force" (1540s, usually of water) probably is the same word, with the connecting notion being "sudden movement," but its senses seem more to fit the older ones of flash (v.), now all transferred to this word except in flash flood, via its variant flushe. OED considers this probably not connected to Old French flux. Transitive sense "cause to flow" is from 1590s.

Meaning "cleanse (a drain, etc.) with a rush of water" is from 1789. Of the face, "become suffused with warm color," from 1680s (flushed). Sense of "inflame with pride or passion" as a result of success, victory, etc., is from 1630s; perhaps influenced in sense by flesh (v). Related: Flushed; flushing.
flush (adj.) Look up flush at Dictionary.com
1550s, "perfect, faultless;" c.1600, "abundantly full," also "full of life or spirit," also "plentifully supplied" (with money, etc.), perhaps from flush (v.1) through the notion of a river running full, hence level with its banks. Meaning "even, level" is from 1620s, originally of ship's decks. In general use by 1791; in typography, 1900; in pugilism, 1812.
flush (n.) Look up flush at Dictionary.com
The section of entries for the various flushes in Century Dictionary opens with a caveat:
The several words spelled flush, being mostly dialectal, colloquial, or technical, and scantily recorded in early literature, have become partly confused with one another, and cannot now be entirely disentangled. Words originally different have acquired some meanings very nearly identical, while on the other hand there are some meanings not obviously related which are, nevertheless, to be referred to one original.
Weekley calls it "A very puzzling word." Sense of "a rush of water" in a stream (1520s), is probably from flush (v.1). From this likely come the extended senses "rush of emotion or passion" (1610s); "a sudden shooting up" (1773); "act of cleansing (a drain) by flushing" (1883); "glow of light or color" (especially sudden redness in the face), 1620s. Independently from the verb, probably, is the noun sense of "a flight of birds suddenly started up" (1590s).

The meaning "hand of cards all of one suit" (1520s) is of uncertain origin, perhaps formed on the model of Middle French flus (15c.), from Old French flux, flus "a flowing, rolling" (see flux), which, in common with its Italian cognate flusso, is said to have once had a sense of "a run" of cards. The form in English probably was influenced by flush (v.1).
flush (v.2) Look up flush at Dictionary.com
"make even or level," 1842, from flush (adj.).
flush (adv.) Look up flush at Dictionary.com
"directly, straight," 1700, from flush (adj.).
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), and thus perhaps distantly related to flush (v.1).
fluster (v.) Look up fluster at Dictionary.com
early 15c. (implied in flostrynge), "bluster, agitate," probably from a Scandinavian source (compare Icelandic flaustr "bustle," flaustra "to bustle"), from Proto-Germanic *flaustra-. Originally "to excite," especially with drink; sense of "to flurry, confuse" is from 1724. Related: Flustered; flustering; flustery. As a noun, 1710, from the verb.
flustrated (adj.) Look up flustrated at Dictionary.com
1712, jocular formation from fluster (v.) + frustrated. Related: Flustration.
flute (n.) Look up flute at Dictionary.com
early 14c., from Old French flaut, flaute (musical) "flute" (12c.), from Old Provençal flaut, of uncertain origin; perhaps imitative or from Latin flare "to blow" (see blow (v.1)); perhaps influenced by Provençal laut "lute." The other Germanic words (such as German flöte) are likewise borrowings from French.

Ancient flutes were direct, blown straight through a mouthpiece but held away from the player's mouth; 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
"grooved, furrowed, ornamented," 1610s, past participle adjective from flute (v.).
flutist (n.) Look up flutist at Dictionary.com
c.1600, probably from French flûtiste (see flute (n.) + -ist); 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 (of birds), to fly before, flicker, float to and fro, be tossed by waves," frequentative of flotian "to float" (see float (v.)). Meaning "throw (someone) into confusion" is from 1660s. Related: Fluttered; fluttering. As a noun, "quick, irregular motion," from 1640s; meaning "state of excitement" is 1740s. Flutterpate "flighty person" is from 1894.
fluvial (adj.) Look up fluvial at Dictionary.com
"pertaining to a river," late 14c., from Latin fluvialis "of a river," from fluvius "a river, stream, running water," related to fluere "to flow" (see flow (v.)).
flux (n.) Look up flux at Dictionary.com
late 14c., "abnormally copious flow," from Old French flus "a flowing, a rolling; a bleeding" (Modern French flux), or directly from Latin fluxus (adj.) "flowing, loose, slack," past participle of fluere "to flow" (see fluent). Originally "excessive flow" (of blood or excrement), it also was 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 "a fly, winged insect," from Proto-Germanic *fleugon "flying insect" (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 (moths, gnats, beetles, locusts, hence butterfly, etc.) and long used by farmers and gardeners for any insect parasite. Flies figuratively for "large numbers" of anything is from 1590s. Plural flien (as in oxen, etc.) gradually normalized 13c.-15c. to -s. Fly in the ointment is from Eccles. x:1. Fly on the wall "unseen observer" first recorded 1881. No flies on _____ "no lack of activity or alertness on the part of," is attested by 1866. Meaning "fish-hook dressed to resemble an insect" is from 1580s; Fly-fishing is from 1650s. Fly-catcher "bird which eats insects on the wing" is from 1670s. The fly agaric mushroom (1788) so called because it was used as a poison for flies.

The sense of "a flight, flying" is from mid-15c. From the verb and the notion of "flapping as a wing does" comes the noun sense of "tent flap" (1810), which was extended to "strip of material sewn into a garment as a covering for buttons" or some other purpose (1844). 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; move through the air with wings," Old English fleogan "to fly, take flight, rise into the air" (class II strong verb; past tense fleag, past participle flogen), from Proto-Germanic *fleugan "to fly" (cognates: Old Saxon fliogan, Old Frisian fliaga, Middle Dutch vlieghen, Dutch vliegen, Old High German fliogan, German fliegen, Old Norse flügja), from PIE *pleuk-, extended form of *pleu- "flowing, floating" (see pluvial).

Meaning "go at full speed" is from c.1300. In reference to flags, 1650s. Transitive sense "cause to move or float in air" (as a flag, kite, etc.) is from 1739; sense of "convey through the air" ("Fly Me to the Moon") is from 1864. Related: Flew; flied (baseball); flown; 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, flion "fly from, avoid, escape;" essentially a variant spelling of flee (q.v.). In Old English, this verb and fleogan "soar through the air with wings" (modern fly (v.1)) differed only in their present tense forms and often were confused, then as now. In some Middle English dialects they seem to have merged completely. Distinguished from one another since 14c. in the past tense: flew for fly (v.1), fled for fly (v.2).
fly (adj.) Look up fly at Dictionary.com
slang, "clever, alert, wide awake," by 1811, 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 by Grose to be an old term of reproach to a woman signifying that she was a witch; used from 1823 in reference to anyone who departs hastily from a recent activity, especially while owing money. The different 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.).
fly-swatter (n.) Look up fly-swatter at Dictionary.com
in reference to a bit of wire mesh on a handle, 1917, from fly (n.) + agent noun from swat (v.). Simple swatter was used in this sense by 1906. Other older names for similar implements were fly-duster (1860), fly-whisk (1836), fly-brush (1823), fly-fan (1821), fly-flap (mid-15c., glossing Latin muscarium).
flyer (n.) Look up flyer at Dictionary.com
also flier, mid-15c., "that which flies, thing or creature that flies," agent noun of fly (v.1). Meaning "something that goes fast" is from 1795. Meaning "speculative investment, financial venture" 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
early 15c., replacing forms from Old English fleogende "flying, winged;" present participle adjective from fly (v.1). The meaning "attached so as to have freedom of movement" (1670s) is the source of the nautical use (flying jib, etc.). Meaning "designed for rapid movement" (especially in military terms) is from 1660s; meaning "passing, hasty, temporary, rapidly constructed" is from 1763.

Flying fish is from 1510s; flying buttress is from 1660s. Flying Dutchman, ghost ship off the Cape of Good Hope, is 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. Flying machine is from 1736 as a theoretical device. Flying saucer first attested 1947, though the image of saucers for unidentified flying objects is from at least 1880s.
Flynn Look up Flynn at Dictionary.com
surname, from Irish flann "red."
flypaper (n.) Look up flypaper at Dictionary.com
also fly-paper, 1851 (the thing 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." Flitecræft was used in Old English for "dialectics."
flyway (n.) Look up flyway at Dictionary.com
"bird migration path," 1891, from fly (v.1) + way (n.).
flywheel (n.) Look up flywheel at Dictionary.com
also fly-wheel, "heavy-rimmed revolving wheel to regulate motion," 1784, from fly (n.) "speed-regulating device" (1590s, 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 volen, 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"), suffixed form of root *pau- (1) "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
Middle English fom, fome (c.1300), from Old English fam "foam, saliva froth; sea," from West Germanic *faimo- (cognates: Old High German veim, German Feim), from PIE root *(s)poi-mo- "foam, froth" (cognates: Sanskrit phenah; Latin pumex "pumice," spuma "foam;" Old Church Slavonic pena "foam;" Lithuanian spaine "a streak of foam"). The plastic variety used in packaging, etc., so called from 1937.
foam (v.) Look up foam at Dictionary.com
Old English famgian "to emit foam, to boil," from the source of foam (n.). Sense of "become foamy, to froth" is from late 14c. Transitive sense is from 1725. Related: Foamed; foaming.
foamy (adj.) Look up foamy at Dictionary.com
Old English faemig "covered with foam;" see foam (n.) + -y (2). Related: Foaminess.
fob (n.) Look up fob at Dictionary.com
1650s, "men's small waist pocket for valuables," of uncertain origin, probably related to Low German fobke "pocket," High German fuppe "pocket," "a dialectal word used in Livonia" [Klein]. Meaning "chain or ornament attached to a watch carried in the fob" is by 1888, shortened from fob chain.
fob (v.) Look up fob at Dictionary.com
"to cheat," late 14c., from obsolete noun fobbe "cheat, trickster" (late 14c.), which perhaps is from Old French forbeter "to deceive, trick, dupe." 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.).

Meaning "to put or shift off (something) by pretense" is from 1650s; to fob (someone) off "put him off deceitfully" is from 1590s. Related: Fobbed; fobbing.
focaccia (n.) Look up focaccia at Dictionary.com
by 1994, from Italian focaccia, from Late Latin focacia, fem. of focacius, used of breads baked under the ashes, from Latin focus "hearth, fireplace" (see focus (n.)). Cognate with Spanish hogaza, Old French foace "griddle cake" (Modern French fouasse "a cake, bun"), Provençal fogassa.
focal (adj.) Look up focal at Dictionary.com
"of or pertaining to a focus," 1690s, from Modern Latin focalis; see focus (n.) + -al (1).
foci (n.) Look up foci at Dictionary.com
classically correct plural of focus (n.).
focus (n.) Look up focus at Dictionary.com
1640s, "point of convergence," 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 optics, "bring into focus" (transitive); 1807 in the figurative sense, from focus (n.). Intransitive use by 1864, originally in photography. Related: Focused; focusing; less commonly focussed; focussing.
fodder (n.) Look up fodder at Dictionary.com
Old English fodder "food," especially "hay, straw, or other bulk food for cattle," from Proto-Germanic *fodram (cognates: Old Norse foðr, Middle Dutch voeder, Old High German fuotar, German Futter), from PIE *pa-trom, suffixed form of *pa- "to feed" (see food).