flagstaff (n.) Look up flagstaff at Dictionary.com
1610s, from flag (n.) + staff (n.). The settlement in Arizona, U.S., so called for a July 4, 1876, celebration in which a large flag was flown from a tall tree.
flagstone (n.) Look up flagstone at Dictionary.com
1730, from flag (n.2) "flat, split stone" + stone (n.).
Flaherty Look up Flaherty at Dictionary.com
surname, Irish Flaithbheartach, literally "Bright-Ruler."
flail (n.) Look up flail at Dictionary.com
"implement for threshing grain," c.1100, perhaps from an unrecorded Old English *flegel, which probably represents West Germanic *flagil (cognates: Middle Dutch and Low German vlegel, Old High German flegel, German flegel), a borrowing of Late Latin flagellum "winnowing tool, flail," from Latin flagellum "whip" (see flagellum).
flail (v.) Look up flail at Dictionary.com
15c., from flail (n.); originally "to scourge;" sense of "to move like a flail" is from 1874. Related: Flailed; flailing.
flair (n.) Look up flair at Dictionary.com
mid-14c., "an odor," from Old French flair "odor or scent," from flairer "to smell," from Vulgar Latin *flagrare, dissimilated from Latin fragrare "emit (a sweet) odor" (see fragrant). Sense of "special aptitude" is American English, 1925, perhaps from notion of a hound's ability to track scent.
flak (n.) Look up flak at Dictionary.com
1938, from German Flak, condensed from Fliegerabwehrkanone, literally "pilot warding-off cannon." Sense of "anti-aircraft fire" is 1940; metaphoric sense of "criticism" is c.1963 in American English.
flake (n.) Look up flake at Dictionary.com
"thin, flat piece," early 14c., possibly from Old English *flacca "flakes of snow," from Old Norse flak "loose or torn piece" (related to Old Norse fla "to skin," see flay), from Proto-Germanic *flago- (cognates: Middle Dutch vlac, Dutch vlak "flat, level," Middle High German vlach, German Flocke "flake"); from PIE *plak- (1) "to be flat," extended form of root *pele- (2) "flat, to spread" (see plane (n.1)).
flake (v.) Look up flake at Dictionary.com
early 15c., "to fall in flakes," from flake (n.). Related: Flaked; flaking.
flaky (adj.) Look up flaky at Dictionary.com
1570s, from flake + -y (2). Meaning "eccentric, crazy" first recorded 1959, said to be American English baseball slang, but probably from earlier druggie slang flake "cocaine" (1920s). Flake "eccentric person" is a 1968 back-formation from it.
The term 'flake' needs explanation. It's an insider's word, used throughout baseball, usually as an adjective; someone is considered 'flaky.' It does not mean anything so crude as 'crazy,' but it's well beyond 'screwball' and far off to the side of 'eccentric.' ["New York Times," April 26, 1964]
flam (n.) Look up flam at Dictionary.com
1630s, "sham story, fabrication" (n.); also "to deceive by flattery" (v.); see flim-flam.
flambe (adj.) Look up flambe at Dictionary.com
1886, of certain types of porcelain, 1906 as a term in cookery, from French flambé, past participle of flamber "to singe, blaze," from Old French flambe "flame" (see flamboyant).
flambeau (n.) Look up flambeau at Dictionary.com
also flambeaux, 1630s, from French flambeau, from flambe "flame" (see flamboyant).
flamboyance (n.) Look up flamboyance at Dictionary.com
1891, from flamboyant + -ance.
flamboyant (adj.) Look up flamboyant at Dictionary.com
1832, first used of a 15c.-16c. architectural style with flame-like curves, from French flamboyant "flaming, wavy," present participle of flamboyer "to flame," from Old French flamboier (12c.), from flambe "flame," from flamble, variant of flamme, from Latin flammula (see flame (n.)). Extended sense of "showy, ornate" is 1879. Related: Flamboyantly.
flame (n.) Look up flame at Dictionary.com
mid-14c., from Anglo-French flaume, Old French flamme (10c.), from Latin flammula "small flame," diminutive of flamma "flame, blazing fire," from PIE *bhleg- "to shine, flash," from root *bhel- (1) "to shine, flash, burn" (see bleach (v.)).

The meaning "a sweetheart" is attested from 1640s; the figurative sense of "burning passion" was in Middle English. Flame-thrower (1917) translates German flammenwerfer (1915).
flame (v.) Look up flame at Dictionary.com
early 14c., flamen, from Old French flamer, from flamme (see flame (n.)). The sense of "unleash invective on a computer network" is from 1980s. Related: Flamed; flaming.
flamen (n.) Look up flamen at Dictionary.com
"ancient Roman priest," 1530s, from Latin flamen, of unknown origin, perhaps from PIE root *bhlad- "to worship" (cognates: Gothic blotan, Old English blotan "to sacrifice"). Also used from early 14c. in reference to the ancient pre-Christian British priests, in imitation of Geoffrey of Monmouth.
flamenco (n.) Look up flamenco at Dictionary.com
1896, from Spanish flamenco, first used of Gypsy dancing in Andalusia. The word means "Fleming, native of Flanders" (Dutch Vlaming) and also "flamingo."

Speculation are varied and colorful about the connection between the bird, the people, and the gypsy dance of Andalusia. Spain ruled Flanders for many years, and King Carlos I brought with him to Madrid an entire Flemish court. One etymology suggests the dance was so called from the bright costumes and energetic movements, which the Spanish associated with Flanders; another is that Spaniards, especially Andalusians, like to name things by their opposites, and because the Flemish were tall and blond and the gypsies short and dark, the gypsies were called "Flemish;" others hold that flamenco was the general Spanish word for all foreigners, gypsies included; or that Flemish noblemen, bored with court life, took to partying with the gypsies.
flamer (n.) Look up flamer at Dictionary.com
agent noun from flame (v.). For homosexual slang sense, see flaming.
flaming (adj.) Look up flaming at Dictionary.com
intensifying adjective, late 19c., from present participle of flame (v.). Meaning "glaringly homosexual" is homosexual slang, 1970s (along with flamer (n.) "conspicuously homosexual man"); but flamer "glaringly conspicuous person or thing" (1809) and flaming "glaringly conspicuous" (1781) are much earlier in the general sense, both originally with reference to "wenches."
flamingo (n.) Look up flamingo at Dictionary.com
1560s, from Portuguese flamengo, Spanish flamengo, literally "flame-colored" (compare Greek phoinikopteros "flamingo," literally "red-feathered"), from Provençal flamenc, from flama "flame" (see flame (n.)) + Germanic suffix -enc "-ing, belonging to."
flammable (adj.) Look up flammable at Dictionary.com
1813, from Latin flammare "to set on fire" (from flamma; see flame) + -able.
flan (n.) Look up flan at Dictionary.com
"open tart," 1846, from French flan "custard tart, cheesecake," from Old French flaon (12c.), from Medieval Latin flado, probably a Germanic borrowing (compare Frankish *flado, Old High German flado "offering cake," Middle High German vlade "a broad, thin cake," Dutch vla "baked custard"), from Proto-Germanic *flatho(n), akin to words for "flat" and probably from PIE root *plat- "to spread" (see place). Borrowed earlier as flawn (c.1300), from Old French.
Flanders Look up Flanders at Dictionary.com
probably a compound of roots represented by Flemish vlakte "plain" + wanderen "to wander."
flaneur (n.) Look up flaneur at Dictionary.com
"loafer, idler," 1854, from French flâneur, from flâner "to stroll, loaf, saunter," probably from a Scandinavian source (compare Norwegian flana, flanta "to gad about").
flange (n.) Look up flange at Dictionary.com
1680s, of unknown origin, perhaps related to Old French flanche "flank, side," fem. of flanc (see flank (n.)).
flank (n.) Look up flank at Dictionary.com
late Old English flanc "fleshy part of the side," from Old French flanc, from Frankish, from Proto-Germanic *hlanca (cognates: Old High German (h)lanca, Middle High German lanke "hip joint," German lenken "to bend, turn, lead"), from PIE root *kleng- "to bend, turn" (see link (n.)). The military sense is first attested 1540s, as is the verb. Related: Flanked; flanking.
flannel (n.) Look up flannel at Dictionary.com
c.1500, probably from Welsh gwlanen "woolen cloth," from gwlan "wool," from Celtic *wlana, from PIE *wele- (1) "wool" (see wool).

The Welsh origin is not a universally accepted etymology, due to the sound changes involved; some (Barnhart, Gamillscheg) suggest the English word is from an Anglo-French diminutive of Old French flaine "a kind of coarse wool." "As flannel was already in the 16th c. a well-known production of Wales, a Welsh origin for the word seems antecedently likely" [OED]. Modern French flanelle is a 17c. borrowing from English.
flap (n.) Look up flap at Dictionary.com
mid-14c., flappe "a blow, slap," probably imitative of the sound of striking. Meaning "something that hangs down" is first recorded 1520s. Sense of "motion or noise like a bird's wing" is 1774; meaning "disturbance, noisy tumult" is 1916, British slang.
flap (v.) Look up flap at Dictionary.com
early 14c., "dash about, shake;" later "strike, hit;" see flap (n.). Meaning "to swing loosely" is from 1520s. Related: Flapped; flapping.
flapdoodle (n.) Look up flapdoodle at Dictionary.com
1833, originally "the stuff they feed fools on" [Marryat]; an arbitrary formation.
flapjack (n.) Look up flapjack at Dictionary.com
pre-1600, from flap + jack (n.), using the personal name in its generic object sense.
flapper (n.) Look up flapper at Dictionary.com
"forward young woman," 1921 slang, from flap (v.), but the exact connection is disputed. Perhaps from flapper "young wild-duck or partridge" (1747), with reference to flapping wings while learning to fly, of which many late 19c. examples are listed in Wright's "English Dialect Dictionary" (1900), including one that defines it as "A young partridge unable to fly. Applied in joke to a girl of the bread-and-butter age."

But other suggested sources are late 19c. northern English dialectal use for "teen-age girl" (on notion of one with the hair not yet put up), or an earlier meaning "prostitute" (1889), which is perhaps from dialectal flap "young woman of loose character" (1610s). Any or all of these might have converged in the 1920s sense. Wright also has flappy, of persons, "wild, unsteady, flighty," with the note that it was also "Applied to a person's character, as 'a flappy lass,'" and further on he lists flappy sket (n.) "an immoral woman."

In Britain the word took on political tones in reference to the debate over voting rights.
"Flapper" is the popular press catch-word for an adult woman worker, aged twenty-one to thirty, when it is a question of giving her the vote under the same conditions as men of the same age. ["Punch," Nov. 30, 1927]
flare (v.) Look up flare at Dictionary.com
mid-16c., originally "spread out" (hair), of unknown origin, perhaps from Dutch vlederen. Related: Flared; flaring. The notion of "spreading out in display" is behind the notion of "spreading gradually outward" (1640s). Flare-up "a sudden burst" is from 1837.
flare (n.) Look up flare at Dictionary.com
"bright, unsteady light," 1814, from flare (v.), which led to the sense of "signal fire" (1883). Flares "flared trousers" is from 1964.
flash (v.) Look up flash at Dictionary.com
late 14c., from flasken (c.1300) "to dash or splash" (as water), probably imitative. Related: Flashed; flashing. Sense of "give off a sudden burst of light or flame" is 1540s. Flash flood is from 1940. Flash card is from 1923. Flash cube (remember those?) is from 1965.
flash (n.) Look up flash at Dictionary.com
1560s, from flash (v.); originally of lightning. Meaning "first news report" is from 1857. Meaning "photographic lamp" is from 1913. The comic book character dates to 1940. Flash in the pan (1809) is from old-style guns, where the powder might ignite in the pan but fail to spark the main charge.
flashback (n.) Look up flashback at Dictionary.com
1903, in reference to fires in engines or furnaces, from flash + back (adj.). Movie plot device sense is from 1916. The hallucinogenic drug sense is attested in psychological literature from 1970, which means probably hippies were using it a few years before.
flasher (n.) Look up flasher at Dictionary.com
"male genital exhibitionist," 1960s (though meat-flasher in this sense was attested in 1890s); agent noun from flash (v.).
flashing (adj.) Look up flashing at Dictionary.com
1570s, of light; present participle adjective from flash (v.).
flashing (n.) Look up flashing at Dictionary.com
"indecent exposure," 1896, verbal noun from flash (v.). The meaning "strip of metal used in roofing, etc." is from 1782, earlier simply flash (1570s), but it is of unknown origin and might be an unrelated word.
flashlight (n.) Look up flashlight at Dictionary.com
American English for what the British might call an electric torch; 1919, from flash + light (n.).
flashpoint (n.) Look up flashpoint at Dictionary.com
also flash point, 1878, from flash (v.) + point (n.). Figurative use by 1955.
flashy (adj.) Look up flashy at Dictionary.com
"showy, cheaply attractive," 1680s, from flash + -y (2). Earlier it meant "splashing" (1580s); "sparkling, giving off flashes" (c.1600). Related: Flashily; flashiness.
flask (n.) Look up flask at Dictionary.com
mid-14c., from Medieval Latin flasco "container, bottle," from Late Latin flasconem "bottle," perhaps from a Germanic source (compare Old English flasce, Old High German flaska, Middle Dutch flasce, German Flasche "bottle"), and if so, perhaps originally meaning "a bottle plaited round, case bottle" (compare Old High German flechtan "to weave," Old English fleohtan "to braid, plait"), from Proto-Germanic base *fleh- (see flax).

Another theory traces it to a metathesis of Latin vasculum. "The assumption that the word is of Teut. origin is chronologically legitimate, and presents no difficulty exc. the absence of any satisfactory etymology" [OED].
flat (adj.) Look up flat at Dictionary.com
early 14c., from Old Norse flatr, from Proto-Germanic *flataz (cognates: Old Saxon flat "flat, shallow,: Old High German flaz "flat, level," Old English flet, Old High German flezzi "floor"), perhaps from PIE *plat- "to spread" (source of Greek platys "broad, flat;" see plaice (n.)).

Sense of "prosaic, dull" is from 1570s; used of drink from c.1600; of musical notes from 1590s, because the tone is "lowered." Flat-out (adv.) "openly, directly" is from 1932; earlier it was a noun meaning "total failure" (1870, U.S. colloquial).
flat (n.) Look up flat at Dictionary.com
1801, from Scottish flat "floor or story of a house," from Old English flet "a dwelling, floor, ground," from the same source as flat (adj.).
flat-footed (adj.) Look up flat-footed at Dictionary.com
c.1600, "with flat feet;" meaning "unprepared" is from 1912, U.S. baseball slang, on notion of "not on one's toes;" earlier in U.S. colloquial use it meant "straightforwardly, downright" (1828), from notion of "standing firmly."
flat-top (n.) Look up flat-top at Dictionary.com
"aircraft carrier," 1943, U.S. Navy, from flat (adj.) + top (n.). As a style of haircut, from 1956.