Online Etymology Dictionary

fishy: late 15c., from fish + -y (2). Sense of "shady, questionable" is first recorded 1840, perhaps from the notion of "slipperiness," or of giving off a bad odor.
fisk (v.): 2002, an Internet argument tactic involving a reprinting of an article or blog post, interlarded with rebuttals and refutations, often intended to show the original is a sandpile of flawed facts, unfounded assertions, and logical fallacies. Named for English journalist Robert Fisk (b.1946), Middle East correspondent for the "Independent," whose writing often criticizes America and Israel and is somewhat noted for looseness with details. Related: Fisked; fisking.
fissile: 1660s, from L. fissilis, from findere (see fissure).
fission: 1841, "division of a cell or organism," from L. fissionem (nom. fissio) "a breaking up, cleaving," from root of findere "to split" (see fissure). Cognate with O.E. bitan "to bite." Nuclear physics sense is 1939.
fissure: c.1400, from O.Fr. fissure, from L. fissura "a cleft," from root of findere "to split, cleave," from PIE *bhi-n-d-, from base *bheid- "to split" (cf. Skt. bhinadmi "I cleave," O.H.G. bizzan "to bite," O.E. bita "a piece bitten off, morsel," O.N. beita "to hunt with dogs," beita "pasture, food").
fist: O.E. fyst, from W.Gmc. *fustiz (cf. O.H.G. fust, O.Fris. fest, M.Du. vuust, Ger. Faust), from P.Gmc. *fukhstiz, probably ultimately from PIE *pengke "five" (cf. O.C.S. pesti, Rus. piasti "fist").
fisticuff: c.1600, from fist + cuff. Related: Fisticuffs.
fistula: "long, narrow ulcer," late 14c., from L. fistula "pipe, ulcer," of uncertain origin.
fit (n.1): 1823, "the fitting of one thing to another," later (1831) "the way something fits." Originally "an adversary of equal power" (mid-13c.), obscure, possibly from O.E. fitt "a conflict, a struggle" (see fit (n.2)). The verb meaning "be suitable" is probably from early 15c. and likely from the adjective. Related: Fitted; fitting.
fit (n.2): "paroxysm, sudden attack" (as of anger), 1540s, probably via M.E. sense of "painful, exciting experience," from O.E. fitt "conflict, struggle," of uncertain origin, with no clear cognates outside English. Phrase by fits and starts first attested 1610s.
fit (adj.): "suited to the circumstances, proper," mid-15c., of unknown origin, perhaps from M.E. noun fit "an adversary of equal power" (mid-13c.), which is perhaps connected to fit (n.1). The verb meaning "to be the right shape" is first attested 1580s. Survival of the fittest (1867) coined by H. Spencer.
fitful: used once by Shakespeare ("Macbeth" iii.2) in sense of "characterized by fits," then revived by Scott (1810) with a sense of "shifting, changing." From fit (n.2) + -ful. Related: Fitfully.
fitness: 1570s, from fit (adj.) + -ness.
fitz: Anglo-Fr. fitz, from O.Fr. fils, from L. filius "son of" (see filial); used regularly in official rolls and hence the first element of many modern surnames; in later times used of illegitimate issue of royalty.
five: O.E. fif, from P.Gmc. *fimfe (cf. O.S. fif, O.N. fimm, O.H.G. funf, Goth. fimf), from PIE *pengke (cf. Skt. panca, Gk. pente, L. quinque, O.C.S. peti, Lith. penke, O.Welsh pimp). Slang five-finger discount "theft" is from 1966.
fiver: 1843 as “five-dollar bill” or “five-pound note.”
fix (v.): late 14c., probably from O.Fr. *fixer, from fixe "fixed," from L. fixus, pp. of figere "to fix, fasten," from PIE base *dhigw- "to stick, to fix." Earliest Eng. usage was to "fix" one's eyes or mind on something; sense of "fasten, attach" is c.1400; that of "settle, assign" is pre-1500 and evolved into "adjust, arrange" (1660s), then "repair" (1737). Sense of "tamper with" (a fight, a jury, etc.) is 1790. As euphemism for "castrate a pet" it dates from 1930. Related: Fixed; fixedly; fixing. The noun meaning "a position from which it is difficult to move" is first recorded 1816, Amer.Eng., from the verb. Meaning "dose of narcotic" is from 1934, originally fix-up, which dates from 1867 in reference to liquor.
fixate (v.): 1926, originally in Freudian theory, a back-formation from fixation. Related: Fixated; fixating.
fixation: late 14c., fixacion, an alchemical word, from M.L. fixationem (nom. fixatio), from fixare "to fix" (see fix). Used in the Freudian sense since 1910.
fixity: 1660s in physics; general use from 1791; see fix + -ity.
fixture: 1590s, “act of fixing,” perhaps from fix on model of mixture. Meaning "anything fixed or securely fastened" is from 1812.
fizz: 1660s, of imitative origin; the noun is recorded from 1812; meaning "effervescent drink" is from 1864.
fizzle: 1530s, "to break wind without noise," probably altered from obsolete fist, from M.E. fisten "break wind" (see feisty). Related: Fizzled; fizzling. Noun sense of "failure, fiasco" is from 1846, originally U.S. college slang for "failure in an exam."
fizzy: 1885, from fizz + -y (2).
fjord: 1670s, from Norw. fiord, from O.N. fjörðr, from N.Gmc. *ferthuz, from PIE *prtus, from *por- "going, passage" (see port (1)).
flab: 1923, back-formation from flabby.
flabbergasted: 1772, mentioned (with bored) in a magazine article as a new vogue word, perhaps from some dialect (in 1823 flabbergast was noted as a Sussex word), likely an arbitrary formation from flabby or flapper and aghast.
flabby: 1690s, variant of flappy, which is recorded in the sense of "softly fleshy" from 1590s; see flap.
flaccid: 1620, from Fr. flaccide, from L. flaccidus "flabby," from flaccus "flabby," of uncertain origin (OED suggests it's onomatopoeic).
flack: "publicity or press agent," 1946, said to have been coined in show biz magazine "Variety" (but this is not the first attested use), supposedly from name of Gene Flack, a movie agent, but influenced by flak.
flag (n.): "cloth ensign," late 15c., now in all modern Germanic languages, but apparently first recorded in English, origin unknown, but likely connected with flag (v.) or else, like it, onomatopoeic. A less likely guess is that it is from the flag in flagstone on notion of being square and flat. 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.): 1540s, "flap about loosely," perhaps a variant of M.E. flakken, flacken "to flap, flutter," probably from O.N. flakka "to flicker, flutter," perhaps onomatopoeic of something flapping in the wind. Sense of "go limp, droop" is first recorded 1610s. Meaning "to designate as someone who will not be served more liquor" is from 1980s, probably from use of flags to signal trains, etc., to halt, which led to the verb in this sense (1856). Related: Flagged; flagging.
flagellant: late 16c., from L. flagellantem, prp. of flagellare (see flagellation).
flagellate (v.): 1620s, from L. flagellatus, pp. of flagellare (see flagellation). Related: Flagellated; flagellating.
flagellation: early 15c., from L. flagellationem (nom. flagellatio) "a scourging," from flagellare, from flagellum "whip," dim. of flagrum "whip, scourge."
flagellum: 1852, from L. flagellum “whip, scourge” (see flagellation).
flagitious: "shamefully wicked, vile, scandalous," late 14c., from O.Fr. flagicieux, from L. flagitiosus, from flagitium "shameful crime," related to flagrum (see flagrant).
flagon: mid-15c., from M.Fr. flacon, from O.Fr. flacon, from L.L. flasconem "bottle" (see flask).
flagrant: c.1500, "resplendent," from L. flagrantem (nom. flagrans) "burning," prp. of flagrare "to burn," from L. root *flag-, corresponding to PIE *bhleg- "to shine, flash, burn" (cf. Gk. phlegein "to burn, scorch"), from base *bhel- (1) (see bleach). Sense of "glaringly offensive" first recorded 1706, probably from common legalese phrase in flagrante delicto "red-handed," lit. "with the crime still blazing." Related: Flagrantly.
flagship: 1670s, ship bearing an admiral's flag, from flag (n.) + ship (n.).
flagstaff: 1610s, from flag (n.) + staff. The settlement in Arizona, U.S., so for a July 4, 1876, celebration in which a large flag was flown from a tall tree.
flagstone: 1730, from flag "flat, split stone" (1604), earlier "piece cut from sod" (1415), from O.N. flaga "stone slab," of unknown origin, perhaps related to O.N. flak (see flake).
Flaherty: Ir. Flaithbheartach, lit. "Bright-Ruler."
flail (n.): "implement for threshing grain," c.1100, from an unrecorded O.E. *flegel, which probably represents W.Gmc. *flagil (cf. M.Du., Low Ger. vlegel, O.H.G. flegel, Ger. flegel), a borrowing of L.L. flagellum "winnowing tool, flail," from L. flagellum "whip." The verb is 15c., from the noun; originally "to scourge;" sense of "to move like a flail" is from 1874. Related: Flailed; flailing.
flair: mid-14c., "an odor," from O.Fr. flair "odor or scent," from flairer "to smell," from L.L. fragrare "emit (a sweet) odor" (see fragrant), with shift of -r- to -l- by dissimilation. Sense of "special aptitude" is Amer.Eng. 1925, perhaps from notion of a hound's ability to track scent.
flak: 1938, from Ger. Flak, acronym for Fliegerabwehrkanone "airplane defense cannon." Sense of "anti-aircraft fire" is 1940; metaphoric sense of "criticism" is c.1963 in Amer.Eng.
flake (n.): early 14c., possibly from O.E. *flacca "flakes of snow," from O.N. flak "loose or torn piece" (related to O.N. fla "to skin," see flay), from P.Gmc. *flak- (cf. M.Du. vlac "flat, level," M.H.G. vlach, Ger. Flocke "flake"); from the same PIE root as L. plaga "a flat surface, district, region." The verb is attested from early 15c. Related: Flaked; flaking.
flaky: 1570s, from flake + -y (2). Meaning "eccentric, crazy" first recorded 1959, said to be Amer.Eng. 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: “sham story, fabrication,” 1630s; as a verb, “to deceive by flattery;” see flim-flam.
flambe: 1886, of certain types of porcelain, 1906 as a term in cookery, from Fr. flambé, pp. of flamber "to singe, blaze," from O.Fr. flambe "flame."