Online Etymology Dictionary

flaw (v.): "cause a flaw or defect in," early 15c. (implied in flawed); see flaw (n.). Related: Flawing.
flawless (n.): 1640s, from flaw (n.) + -less. Related: Flawlessly; flawlessness. Flawful (1881) probably exists only as a jocular formation.
flax (n.): Old English fleax "flax plant; cloth made with flax, linen," from Proto-Germanic *flakhsan (source also of Old Frisian flax, Middle Dutch and Dutch vlas, Old Saxon flas, Old High German flahs, German Flachs), probably from Proto-Germanic base *fleh- "to plait," corresponding to PIE *plek- "to weave, to plait" (see ply (v.1)). But some connect it with PIE *pleik- (see flay) from the notion of "stripping" fiber to prepare it.
flaxen (adj.): "made of flax," mid-15c., from flax + -en (2). As "of the color of flax" (usually with reference to hair) it is attested from 1520s.
flaxseed (n.): also flax-seed, 1560s, from flax + seed (n.).
flay (v.): Old English flean "to skin, to flay" (strong verb, past tense flog, past participle flagen), from Proto-Germanic *flahan (source also of Middle Dutch vlaen, Old High German flahan, Old Norse fla), from PIE root *pl(e)ik-, *pleik- "to tear, rend" (source also of Lithuanian plešiu "to tear"). Related: Flayed; flaying.
flea (n.): Old English flea "flea," from Proto-Germanic *flauhaz (source also of Old Norse flo, Middle Dutch vlo, German Floh), perhaps related to Old English fleon "to flee," with a notion of "the jumping parasite," but more likely from PIE *plou- "flea" (source also of Latin pulex, Greek psylla; see puce).

Chaucer's plural is fleen. Flea-bag "bed" is from 1839; flea-circus is from 1886; flea-collar is from 1953. Flea-pit (1937) is an old colloquial name for a movie-house, or, as OED puts it, "an allegedly verminous place of public assembly."
"A man named 'Mueller' put on the first trained-flea circus in America at the old Stone and Austin museum in Boston nearly forty years ago. Another German named 'Auvershleg' had the first traveling flea circus in this country thirty years ago. In addition to fairs and museums, I get as high as $25 for a private exhibition." ["Professor" William Heckler, quoted in "Popular Mechanics," February 1928. Printed at the top of his programs were "Every action is visible to the naked eye" and "No danger of desertion."]
flea (v.): "clear of fleas," c. 1600, from flea (n.). Related: Flead.
flea market (n.): 1917, especially in reference to the marché aux puces in Paris, so-called "because there are so many second-hand articles sold of all kinds that they are believed to gather fleas." [E.S. Dougherty, "In Europe," 1922].
flea-bite (n.): mid-15c., figurative, "something that causes but slight pain," from flea (n.) + bite (n.). Related: Flea-bitten (1560s); flea-biting (verbal noun), 1550s.
fleabane (n.): also flea-bane, 1540s, from flea (n.) + bane (n.). Old English had fleawyrt, used of various plants supposed to destroy fleas.
fleam (n.): "sharp instrument for opening veins in bloodletting," late Old English, from Old French flieme (Modern French flamme), from Medieval Latin fletoma, from Late Latin flebotomus, from Greek phlebotomos "a lancet" (see phlebotomy).
fleck (v.): late 14c., "to spot, stain, cover with spots," probably from Old Norse flekka "to spot," from Proto-Germanic *flekk- (source also of Middle Dutch vlecke, Old High German flec, German Fleck), from PIE *pleik- "to tear" (see flay). Related: Flecked; flecking.
fleck (n.): 1590s, "a mark on skin, a freckle," of uncertain origin; perhaps from fleck (v.) or else from a related word elsewhere in Germanic, such as Middle Dutch vlecke or Old Norse flekkr "a fleck, spot." From 1750 as "small particle," 1804 as "a patch, a spot" of any kind.
fled: past tense and past participle of flee (q.v.) and fly (v.2).
fledge (v.): "to acquire feathers," 1560s, from Old English adjective *-flycge (Kentish -flecge; in unfligge "featherless," glossing Latin implumes) "having the feathers developed, fit to fly," from Proto-Germanic *flugja- "ready to fly" (source also of Middle Dutch vlugge, Low German flügge), from PIE *pleuk- "to fly" (see fletcher). Meaning "bring up a bird" (until it can fly on its own) is from 1580s. Related: Fledged; fledging.
fledged (adj.): "furnished with feathers," 1570s (in full-fledged), thus "developed, matured, able to fly;" past-participle adjective from fledge (v.).
fledgling: also fledgeling, 1830, "untried" (adj.), in Tennyson; 1846 as a noun meaning "young bird" (one newly fledged); from fledge + diminutive suffix -ling. Of persons, from 1856.
flee (v.): Old English fleon, flion "take flight, fly from, avoid, escape" (contracted class II strong verb; past tense fleah, past participle flogen), from Proto-Germanic *fleuhan "to run away" (source also of Old High German fliohan, Old Norse flöja, Old Frisian flia, Dutch vlieden, German fliehen, Gothic þliuhan "to flee"), probably from PIE *pleuk-, extended form of root *pleu- "to flow" (see pluvial). Also compare fly (v.2).

Weak past tense and past participle fled emerged in Middle English under influence of Scandinavian. Old English had a transitive form, geflieman "put to flight, banish, drive away," which came in handy in the Anglo-Saxon Chronicle. Related: fled; Fleeing.
fleece (n.): "wool coat of a sheep," Old English fleos, flies "fleece, wool, fur, sealskin," from West Germanic *flusaz (source also of Middle Dutch vluus, Dutch vlies, Middle High German vlius, German Vlies), which is of uncertain origin; probably from PIE *pleus- "to pluck," also "a feather, fleece" (source also of Latin pluma "feather, down," Lithuanian plunksna "feather").
fleece (v.): 1530s in the literal sense of "to strip (a sheep) of fleece," from fleece (n.). From 1570s in the figurative meaning "to cheat, swindle, strip of money." Related: Fleeced; fleecer; fleecing.
fleecy (adj.): 1560s, "woolly," from fleece (n.) + -y (2). From 1630s as "resembling fleece" in any sense (originally by Milton, of clouds).
fleer (v.): "grin mockingly," c. 1400, perhaps from Scandinavian (compare dialectal Norwegian flira "giggle, laugh at nothing," dialectal Danish flire "to grin, sneer, titter"). Transitive sense from 1620s. Related: Fleered; fleering; fleeringly. As a noun from c. 1600.
fleer (n.): "one who flees," late 14c., agent noun from flee (v.).
fleet (n.): Old English fleot "a ship, raft, floating vessel," also, collectively, "means of sea travel; boats generally," from fleotan "to float" (see fleet (v.)). Sense of "naval force, group of ships under one command" is in late Old English. The more usual Old English word was flota "a ship," also "a fleet; a sailor." The fleet for "the navy" is from 1712.

The Old English word also meant "estuary, inlet, flow of water," especially the one into the Thames near Ludgate Hill, which lent its name to Fleet Street (home of newspaper and magazine houses, standing for "the English press" since 1882), Fleet prison (long used for debtors), etc.
fleet (adj.): "swift," 1520s, but probably older than the record; apparently from or cognate with Old Norse fliotr "swift," from Proto-Germanic *fleuta, which is related to the source of fleet (v.). Related: Fleetness.
fleet (v.): Old English fleotan "to float; drift; flow, run (as water); swim; sail (of a ship)," from Proto-Germanic *fleutan (source also of Old Frisian fliata, Old Saxon fliotan "to flow," Old High German fliozzan "to float, flow," German fliessen "to flow, run, trickle" (as water), Old Norse fliota "to float, flow"), from PIE root *pleu- "to flow, swim" (see pluvial).

Meaning "to glide away like a stream, vanish imperceptibly" is from c. 1200; hence "to fade, to vanish" (1570s). Related: Fleeted; fleeting.
fleeting (adj.): early 13c., "fickle, shifting, unstable," from Old English fleotende "floating, drifting," later "flying, moving swiftly," from present participle of fleotan "to float, drift, flow" (see fleet (v.)). Meaning "existing only briefly" is from 1560s. Related: Fleetingly.
Fleming (n.): from Old English Flæming "native or inhabitant of Flanders," from Old Dutch Vlaemingh, Old Frisian Fleming, both from Proto-Germanic *Flam- (see Flanders). The Germanic name was borrowed in Medieval Latin as Flamingus, hence Spanish Flamenco, Provençal Flamenc, etc. French has flandrin "a lanky lad" (15c.), originally a nickname of a Fleming, thence "any tall and meagre man," as they were thought to be [Kitchin].
Flemish (adj.): "pertaining to or native to Flanders," early 14c., flemmysshe, probably from Old Frisian Flemische, or a native formation from Fleming + -ish.
flense (v.): also flench, 1814, from Danish flense, perhaps, with other Germanic fli- words for "cutting, splitting" (for example flint, flinders) ultimately from PIE root *(s)plei- "to splice, split." Related: Flenser; flensing.
flesh (n.): Old English flæsc "flesh, meat, muscular parts of animal bodies; body (as opposed to soul)," also "living creatures," also "near kindred" (a sense now obsolete except in phrase flesh and blood), common West and North Germanic (compare Old Frisian flesk, Middle Low German vlees, German Fleisch "flesh," Old Norse flesk "pork, bacon"), which is of uncertain origin; according to Watkins, perhaps from Proto-Germanic *flaiskjan "piece of meat torn off," from PIE *pleik- "to tear."

Of fruits from 1570s. Figurative use for "carnal nature, animal or physical nature of man" (Old English) is from the Bible, especially Paul's use of Greek sarx, and this led to sense of "sensual appetites" (c. 1200).

Flesh-wound is from 1670s; flesh-color, the hue of "Caucasian" skin, is first recorded 1610s, described as a tint composed of "a light pink with a little yellow" [O'Neill, "Dyeing," 1862]. In the flesh "in a bodily form" (1650s) originally was of Jesus (Wyclif has up the flesh, Tindale after the flesh). An Old English poetry-word for "body" was flæsc-hama, literally "flesh-home." A religious tract from 1548 has fleshling "a sensual person." Flesh-company (1520s) was an old term for "sexual intercourse."
flesh (v.): 1520s, "to render (a hunting animal) eager for prey by rewarding it with flesh from a kill," with figurative extensions, from flesh (n.). Meaning "to clothe or embody with flesh," with figurative extensions, is from 1660s. Related: Fleshed; fleshing.
fleshless (adj.): 1580s, from flesh (n.) + -less.
fleshly (adj.): Old English flæsclic "corporeal, carnal;" see flesh (n.) + -ly (1).
fleshpot (n.): from flesh (n.) + pot (n.1); literally "pot in which flesh is boiled," hence "luxuries regarded with envy," especially in fleshpots of Egypt, from Exodus xvi:3:
Whan we sat by ye Flesh pottes, and had bred ynough to eate. [Coverdale translation, 1535]
fleshy (adj.): late 14c., "consisting of muscle and flesh," also "plump," from flesh (n.) + -y (2). Related: Fleshiness.
fletch (v.): "fit feathers to" (an arrow), 1650s, variant of fledge (v.) in sense "fit (an arrow) with feathers, altered by influence of fletcher. Related: Fletched; fletching.
fletcher (n.): "arrow-maker," early 14c. (as a surname attested from 1203), from Old French flechier "maker of arrows," from fleche "arrow," which is probably from Frankish, from Proto-Germanic *fleug-ika- (compare Old Low German fliuca, Middle Dutch vliecke), from PIE *pleuk- "to fly," extended form of root *pleu- "to flow" (see pluvial).
fletcherism (n.): dietary system emphasizing very thorough mastication, 1903, from -ism + name of Horace Fletcher (1849-1919), U.S. health enthusiast. Related: Fletcherize; fletcherized.
fleur-de-lis (n.): also fleur-de-lys, mid-14c., from Anglo-French flour de lis "lily-flower," from Old French, literally "flower of the iris," especially borne as a heraldic device on the royal arms of France. There is much dispute over what it is meant to resemble; perhaps an iris flower, or the head of a scepter, or a weapon of some sort. In Middle English often taken as flour delice "flower of joy, lovely flower" (hence Anglo-Latin flos deliciae); also flour de luce "flower of light" (as if from Latin lucem).
fleuret (n.): "ornament in the form of a small flower," 1811, from French fleurette "small flower," diminutive of fleur "flower, blossom" (see flower (n.)). As a type of small sword from 1640s.
fleuron (n.): "flower-shaped ornament," late 14c., floroun, from Old French floron (Modern French fleuron), from flor "flower" (see flower (n.)). Spelling modified 17c. in English based on French.
flew: past tense of fly (v.1).
flex (v.): 1520s, "to bend," usually of muscles, probably a back-formation from flexible. Related: Flexed; flexing.
flexibility (n.): 1610s, of physical things, from French flexibilité (in Old French, "weakness, vacillation") or directly from Late Latin flexibilitatem (nominative flexibilitas), from Latin flexibilis "pliant, yielding" (see flexible). Of immaterial things from 1783.
flexible (adj.): early 15c., "capable of being bent; mentally or spiritually pliant," from Middle French flexible or directly from Latin flexibilis "that may be bent, pliant, flexible, yielding;" figuratively "tractable, inconstant," from flex-, past participle stem of flectere "to bend," which is of uncertain origin. Flexile (1630s) and flexive (1620s) have become rare. Related: Flexibly. Coles' dictionary (1717) has flexiloquent "speaking words of doubtful or double meaning."
flexion (n.): c. 1600, "bent part," also, in grammar, "modification of part of a word," from Latin flexionem (nominative flexio) "a bending, swaying; bend, turn, curve," noun of action from past participle stem of flectere "to bend" (see flexible). Flection (18c.) is more recent, less etymological, but said to be more common in modern English, perhaps by influence of affection, direction, where the -ct- is in the Latin word. According to some modern dictionaries, flexion is "confined to anatomical contexts." Related: Flexional; flectional.
flexography (n.): type of rotary printing technique, 1952, from comb. form of flexible (in reference to the plate used) + -graphy in the literal sense.
flexor (n.): 1610s, of muscles, Modern Latin, agent noun from stem of Latin flectere "to bend" (see flexible). Alternative form flector attested from 1660s (see flexion).