flaccid (adj.) Look up flaccid at Dictionary.com
1610s, from French flaccide or directly from Latin flaccidus "flabby, pendulous, weak, drooping," from flaccus "flabby, flap-eared," which is of uncertain origin (OED suggests it's imitative). Related: Flaccidly; flacidness; flaccidity; flaccescency.
flack (n.) Look up flack at Dictionary.com
"publicity or press agent," 1945, also by that year as a verb, said to have been coined at show biz magazine "Variety" (but the first attested use is not in "Variety") and supposedly from name of Gene Flack, a movie agent, but influenced by flak. There was a Gene Flack who was an advertising executive in the U.S. during the 1940s, but he seems to have sold principally biscuits, not movies.
flag (n.1) Look up flag at Dictionary.com
"cloth ensign," late 15c., now in all modern Germanic languages (German Flagge, Dutch vlag, Danish flag, Swedish flagg, etc.) but apparently first recorded in English, of unknown origin, but likely connected to flag (v.1) or else an independent imitative formation "expressing the notion of something flapping in the wind" [OED]. A guess considered less likely is that it is from flag (n.2) on the notion of being square and flat.

Meaning "name and editorial information on a newspaper" is by 1956. U.S. Flag Day (1894) is in reference to the adopting of the Stars and Stripes by the Continental Congress on June 14, 1777.
flag (v.1) Look up flag at Dictionary.com
1540s, "flap about loosely," probably a later variant of Middle English flakken, flacken "to flap, flutter" (late 14c.), which probably is from Old Norse flaka "to flicker, flutter, hang losse," perhaps imitative of something flapping lazily in the wind. Sense of "go limp, droop, become languid" is first recorded 1610s. Related: Flagged; flagging.
flag (n.2) Look up flag at Dictionary.com
"flat stone for paving," c. 1600, ultimately from Old Norse flaga "stone slab," from Proto-Germanic *flago- (see flake (n.)). Earlier in English as "piece cut from turf or sod" (mid-15c.), from Old Norse flag "spot where a piece of turf has been cut out," from flaga.
flag (n.3) Look up flag at Dictionary.com
plant growing in moist places, late 14c., "reed, rush," perhaps from Scandinavian (compare Danish flæg "yellow iris") or from Dutch flag; perhaps ultimately connected to flag (v.1) on notion of "fluttering in the breeze."
flag (v.2) Look up flag at Dictionary.com
1875, "place a flag on or over," from flag (n.1). Meaning "designate as someone who will not be served more liquor," by 1980s, probably from use of flags to signal trains, etc., to halt, which led to a verb meaning "inform by means of signal flags" (1856, American English). Meaning "to mark so as to be easily found" is from 1934 (originally by means of paper tabs on files). Related: Flagged; flagging.
flagellant (n.) Look up flagellant at Dictionary.com
late 16c., "one who whips or scourges himself for religious discipline," from Latin flagellantem (nominative flagellans), present participle of flagellare "to scourge, lash" (see flagellum). There were notable outbreaks of it in 1260 and 1340s. As an adjective, "given to flagellation," 1880.
flagellate (v.) Look up flagellate at Dictionary.com
"to whip, scourge," 1620s, from Latin flagellatus, past participle of flagellare "to scourge, lash" (see flagellum). Related: Flagellated; flagellating. An earlier verb for this in English was flagellen (mid-15c.; see flail (v.)).
flagellate (adj.) Look up flagellate at Dictionary.com
1851, from flagellum + -ate (1).
flagellation (n.) Look up flagellation at Dictionary.com
early 15c., "the scourging of Christ," from Old French flagellacion "scourging, flogging," or directly from Latin flagellationem (nominative flagellatio) "a scourging," noun of action from past participle stem of flagellare "to scourge, lash" (see flagellum). In a general sense from 1520s.
flagellum (n.) Look up flagellum at Dictionary.com
"long, lash-like appendage," 1837, from Latin flagellum "whip, scourge," also figurative, diminutive of flagrum "a whip," from PIE root *bhlag- "to strike" (cognates: Latin flagitium "shameful act, passionate deed, disgraceful thing," flagitare "to demand importunately;" Old Norse blakra "to flutter with the wings," blekkja "to impose upon;" Lithuanian blaškau "to and fro").
flageolet (n.) Look up flageolet at Dictionary.com
flute-like instrument, 1650s, from French flageolet, diminutive of Old French flajol, from Provençal flajol, which is of unknown origin.
flagitious (adj.) Look up flagitious at Dictionary.com
"shamefully wicked, criminal," late 14c., from Old French flagicieus or directly from Latin flagitiosus "shameful, disgraceful, infamous," from flagitium "shameful act, passionate deed, disgraceful thing," related to flagrum "a whip, scourge, lash," and flagitare "to demand importunately," all from PIE root *bhlag- "to strike" (see flagellum). Related: Flagitiously; flagitiousness.
flagman (n.) Look up flagman at Dictionary.com
also flag-man, "signaler," 1832, from flag (n.1) + man (n.). Earlier it meant "admiral" (1660s).
flagon (n.) Look up flagon at Dictionary.com
"large bottle for wine or liquor," mid-15c., from Middle French flacon, Old French flascon "small bottle, flask" (14c.), from Late Latin flasconem (nominative flasco) "bottle" (see flask).
flagpole (n.) Look up flagpole at Dictionary.com
also flag-pole, 1782, from flag (n.1) + pole (n.1). Flagpole-sitting as a craze is attested from 1927.
flagrance (n.) Look up flagrance at Dictionary.com
"glaring shamefulness," 1610s, from French flagrance or directly from Latin flagrantia "a glow, ardor, a burning desire," noun of quality from flagrantem "burning, blazing, glowing" (see flagrant). Related: Flagrancy (1590s).
flagrant (adj.) Look up flagrant at Dictionary.com
c. 1500, "resplendent" (obsolete), from Latin flagrantem (nominative flagrans) "burning, blazing, glowing," figuratively "glowing with passion, eager, vehement," present participle of flagrare "to burn, blaze, glow" from Proto-Italic *flagro- "burning" (cognates: Oscan flagio-, an epithet of Iuppiter), corresponding to PIE *bhleg-ro-, from *bhleg- "to shine, flash, burn" (cognates: Greek phlegein "to burn, scorch," Latin fulgere "to shine"), from root *bhel- (1) "to shine, flash, burn" (see bleach (v.)). Sense of "glaringly offensive, scandalous" (rarely used of persons) first recorded 1706, probably from common legalese phrase flagrante delicto "while the crime is being committed, red-handed," literally "with the crime still blazing." Related: Flagrantly.
flagship (n.) Look up flagship at Dictionary.com
also flag-ship, 1670s, a warship bearing the flag of an admiral, vice-admiral, or rear-admiral, from flag (n.) + ship (n.). Properly, at sea, a flag is the banner by which an admiral is distinguished from the other ships in his squadron, other banners being ensigns, pendants, standards, etc. Figurative use by 1933.
flagstaff (n.) Look up flagstaff at Dictionary.com
1610s, from flag (n.) + staff (n.). The settlement in Arizona, U.S., said to have been 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
"any rock which splits easily into flags," 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, if it existed, probably is from West Germanic *flagil (cognates: Middle Dutch and Low German vlegel, Old High German flegel, German flegel), a West Germanic borrowing of Late Latin flagellum "winnowing tool, flail," in classical Latin "a whip" (see flagellum).
flail (v.) Look up flail at Dictionary.com
mid-15c., "to whip, scourge," from flail (n.). Sense of "to move like a flail" is from 1873. Related: Flailed; flailing.
flair (n.) Look up flair at Dictionary.com
mid-14c., "an odor," from Old French flaire "odor or scent," especially in hunting, "fragrance, sense of smell," from flairier "to give off an odor; stink; smell sweetly" (Modern French flairer), from Vulgar Latin *flagrare, dissimilated from Latin fragrare "emit (a sweet) odor" (see fragrant). Sense of "special aptitude" is American English, 1925, probably from hunting and the notion of a hound's ability to track scent.
flak (n.) Look up flak at Dictionary.com
1938, "anti-aircraft gun," from German Flak, condensed from Fliegerabwehrkanone, literally "pilot warding-off cannon." Sense of "anti-aircraft fire" is from 1940; metaphoric sense of "criticism" is c. 1963 in American English. Flak jacket is by 1956.
flake (n.) Look up flake at Dictionary.com
"thin, flat piece of snow; a particle," early 14c., also flauke, flagge, which is of uncertain origin, possibly from Old English *flacca "flakes of snow," or from cognate Old Norse flak "loose or torn piece" (related to Old Norse fla "to skin;" see flay); or perhaps 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" (see placenta). From late 14c. as "a speck, a spot."
flake (v.) Look up flake at Dictionary.com
early 15c., flaken, (of snow) "to fall in flakes," from flake (n.). Transitive meaning "break or peel off in flakes" is from 1620s; intransitive sense of "to come off in flakes" is from 1759. . Related: Flaked; flaking.
flaky (adj.) Look up flaky at Dictionary.com
1570s, "consisting of flakes," 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 (n.) "eccentric person" is a 1968 back-formation from it. Related: Flakiness.
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," also as a verb, "to deceive by flattery;" see flim-flam.
flambe (adj.) Look up flambe at Dictionary.com
1869, of certain types of porcelain, 1914 as a term in cookery, from French flambé, past participle of flamber "to singe, blaze" (16c.), from Old French flambe "a flame" (see flamboyant). Middle English had flame (v.) in cookery sense "baste (a roast) with hot grease, to baste; to glaze (pastry)."
flambeau (n.) Look up flambeau at Dictionary.com
also flambeaux, 1630s, "flaming torch," from French flambeau (14c.), from flambe "flame" (see flamboyant). By 1883 as "a large, decorative candlestick."
flamboyance (n.) Look up flamboyance at Dictionary.com
1849, from flamboyant + -ance. Related: Flamboyancy (1846).
flamboyant (adj.) Look up flamboyant at Dictionary.com
1832, originally in reference to a 15c.-16c. architectural style with wavy, flame-like curves, from French flamboyant "flaming, wavy," present participle of flamboyer "to flame," from Old French flamboiier "to flame, flare, blaze, glow, shine" (12c.), from flambe "a flame, flame of love," from flamble, variant of flamme, from Latin flammula "little flame" (see flame (n.)). Extended sense of "showy, ornate" is from 1879. Related: Flamboyantly.
flame (n.) Look up flame at Dictionary.com
Middle English flaume, also flaumbe, flambe, flame, flamme, mid-14c., "a flame;" late 14c., "a flaming mass, a fire; fire in general, fire as an element;" also figurative, in reference to the "heat" or "fire" of emotions, from Anglo-French flaume, flaumbe "a flame" (Old French flambe, 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, object of one's passion" is attested from 1640s; the figurative sense of "burning passion" was in Middle English, and the nouns in Old French and Latin also meant "fire of love, flame of passion," and, in Latin "beloved object." The Australian flame-tree is from 1857, so called for its red flowers.
flame (v.) Look up flame at Dictionary.com
Middle English flaumen, also flaumben, flomben, flamben, flamen, flammen, c. 1300 (implied in flaming "to shine (like fire), gleam, sparkle like flames;" mid-14c. as "emit flames, be afire, to blaze," from Anglo-French flaumer, flaumber (Old French flamber) "burn, be on fire, be alight" (intransitive), from flamme "a flame" (see flame (n.)).

Transitive meaning "to burn, set on fire" is from 1580s. Meaning "break out in violence of passion" is from 1540s; the sense of "unleash invective on a computer network" is from 1980s. Related: Flamed; flaming. To flame out, in reference to jet engines, is from 1950.
flame-thrower (n.) Look up flame-thrower at Dictionary.com
also Flamethrower, 1917, translating German flammenwerfer (1915). See flame (n.) + throw (v.).
flamen (n.) Look up flamen at Dictionary.com
"ancient Roman priest," 1530s, from Latin flamen "a priest of one deity," which is of unknown origin, perhaps from PIE root *bhlad- "to worship" (cognates: Gothic blotan, Old English blotan "to sacrifice"). Also used from early 14c., in imitation of Geoffrey of Monmouth, in reference to ancient pre-Christian British priests. Related: Flamineous.
The old connection of flamen with Skt. brahman- is highly problematic, and has been dismissed by Schrijver. As WH surmise, the ending -en points to an archaism, probably a n[euter] noun "sacrificial act" which changed its semantics to 'priest'; for a similar shift, cf. augur "bird-observer" .... The only viable comparanda are found in [Germanic], but they show root-final (or suffixal) *-d~. [de Vaan]
flamenco (n.) Look up flamenco at Dictionary.com
1882, from Spanish flamenco, first used of Gypsy dancing in Andalusia. The word in Spanish meant "a 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 in 16c., 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 slumming among the gypsies. Compare Gypsy.
flamer (n.) Look up flamer at Dictionary.com
1590s, agent noun from flame (v.). Figurative sense "glaringly conspicuous person" is from 1809. For homosexual slang sense, see flaming.
flaming (adj.) Look up flaming at Dictionary.com
late 14c., "flame-like in appearance;" c. 1400, "on fire," present participle adjective from flame (v.). Meaning "of bright or gaudy colors" is from mid-15c. As an intensifying adjective, late 19c. 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 a general sense, both originally with reference to "wenches." Related: Flamingly.
flamingo (n.) Look up flamingo at Dictionary.com
long-legged, long-necked brightly colored pink bird of the tropical Americas, 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." Perhaps accommodated to words for Fleming (see flamenco).
flammable (adj.) Look up flammable at Dictionary.com
1813, from stem of Latin flammare "to set on fire" (from flamma; see flame (n.)) + -able. In modern (20c.) use, a way to distinguish from the ambiguity of inflammable.
flan (n.) Look up flan at Dictionary.com
"open tart," 1846, from French flan "custard tart, cheesecake," from Old French flaon "flat-cake, tart, flan" (12c.), from Medieval Latin flado (10c.), which probably is from Frankish *flado or another Germanic source (compare Old High German flado "offering cake," Middle High German vlade "a broad, thin cake," Dutch vla "baked custard"), from Proto-Germanic *flatho(n) "flat cake," probably from PIE root *plat- "to spread" (see plaice (n.)). Borrowed earlier as flawn (c. 1300), from Old French.
Flanders Look up Flanders at Dictionary.com
from a source akin to Dutch Vlaanderen probably a compound of roots represented by Flemish vlakte "plain" + wanderen "to wander."
flaneur (n.) Look up flaneur at Dictionary.com
"habitual loafer, idle man about town," 1854, from French flâneur, from flâner "to stroll, loaf, saunter," probably from a Scandinavian source (compare Old Norse flana "to wander aimlessly," Norwegian flana, flanta "to gad about"), perhaps from PIE *pele- (2) "flat, to spread." Related: flânerie.
flange (n.) Look up flange at Dictionary.com
1680s, "a widening or branching out," of unknown origin, perhaps related to Old French flanche "flank, hip, side," fem. of flanc (see flank (n.)). Meaning "projecting rim, etc., used for strength or guidance" is from 1735. As a verb from 1820.
flank (n.) Look up flank at Dictionary.com
late Old English flanc "flank, fleshy part of the side," from Old French flanc "hip, side," from Frankish or another Germanic source, from Proto-Germanic *hlanca- (cognates: Old High German (h)lanca, Middle High German lanke "hip joint," German lenken "to bend, turn aside;" Old English hlanc "loose and empty, slender, flaccid;" Old Norse hlykkr "a bend, noose, loop"), from PIE root *kleng- "to bend, turn" (see link (n.)). Showing characteristic change of Germanic hl- to Romanic fl-. The military sense is first attested 1540s. Meaning "side" of anything is by 1620s. As an adjective, "pertaining to the flank or side," 1660s. Related: Flanked; flanking.
flank (v.) Look up flank at Dictionary.com
1590s (military), "to guard the flank," also, "to menace the flank, fire sideways upon," from flank (n.). Meaning "stand or be placed at the side of" is from 1650s. Related: Flanked; flanking.