Online Etymology Dictionary

fawney (n.): 1781, from Irish fainne "ring."
fax (n.): 1948, short for facsimile (telegraphy). The verb attested by 1970. Related: Faxed; faxing.
fay (n.): "fairy," late 14c., from Old French fae (12c., Modern French fée), from Vulgar Latin *fata "goddess of fate," fem. singular of Latin fata (neuter plural), literally "the Fates" (see fate). Adjective meaning "homosexual" is attested from 1950s.
Fay: fem. proper name, in some cases from Middle English fei, Old French fei "faith," or else from fay "fairy."
faze (v.): 1830, American English variant of Kentish dialect feeze "to frighten, alarm, discomfit" (mid-15c.), from Old English fesian, fysian "drive away," from Proto-Germanic *fausjanan (cf. Swedish fösa "drive away," Norwegian föysa). Related: Fazed; fazing.
FBI: U.S. Federal Bureau of Investigation, formed 1935 from the former United States Bureau of Investigation (1908).
FCC: U.S. Federal Communications Commission, formed 1934 from the former Federal Radio Commission.
FDA: U.S. Food and Drug Administration, 1930, shortened from Food, Drug, and Insecticide Administration.
feal (v.): "to hide, conceal," early 14c., a Northern English and Northern Midlands word, from Old Norse fela "to hide," cognate with Gothic filhan "to hide, bury," Old English feolan.
feal (adj.): "faithful," 1560s, from Old French feal, collateral form of feeil, from Latin fidelis "loyal" (see fidelity).
fealty (n.): c.1300, from Old French feauté "loyalty, fidelity; homage sworn by a vassal to his overlord; faithfulness," from Latin fidelitatem (nominative fidelitas) "fidelity," from fidelis "loyal, faithful" (see fidelity).
fear (n.): Old English fær "calamity, sudden danger, peril," from Proto-Germanic *feraz "danger" (cf. Old Saxon far "ambush," Old Norse far "harm, distress, deception," Dutch gevaar, German Gefahr "danger"), from PIE root *per- "to try, risk, come over, go through" (perhaps connected with Greek peira "trial, attempt, experience," Latin periculum "trial, risk, danger").

Sense of "uneasiness caused by possible danger" developed late 12c. Old English words for "fear" as we now use it were ege, fyrhto; as a verb, ondrædan.
fear (v.): Old English færan "terrify, frighten," originally transitive (sense preserved in archaic I fear me and somewhat revived in digital gaming). Meaning "feel fear" is late 14c. Cognate with Old Saxon faron "to lie in wait," Middle Dutch vaeren "to fear," Old High German faren "to plot against," Old Norse færa "to taunt." See fear (n.). Related: Feared; fearing.
fearful (adj.): mid-14c., "causing fear," from fear + -ful. Meaning "full of fear, timid" (now less common) also is from mid-14c. As a mere emphatic, from 1630s. Related: Fearfully; fearfulness.
fearless (adj.): early 15c., from fear (n.) + -less. Related: Fearlessly; fearlessness.
fearsome (adj.): 1768, from fear + -some. Related: Fearsomely; fearsomeness.
feasance (n.): 1530s, from Anglo-French fesance, from Old French faisance "action, deed, enactment," from faisant, present participle of faire "to make, do" (from Latin facere; see factitious).
feasibility (n.): 1620s, from feasible + -ity.
feasible (adj.): "capable of being done, accomplished or carried out," mid-15c., from Anglo-French faisible, from Old French faisable "possible, easy, convenient," from fais-, stem of faire "do, make," from Latin facere "do, perform" (see factitious). Fowler recommends this word only for those "who feel that the use of an ordinary word for an ordinary notion does not do justice to their vocabulary or sufficiently exhibit their cultivation."
feasibly (adv.): 1640s, from feasible + -ly (2).
feast (v.): c.1300, "partake of a feast," from Old French fester, from feste (see feast (n.)). Related: Feasted; feasting.
feast (n.): c.1200, "religious anniversary characterized by rejoicing" (rather than fasting), from Old French feste (12c., Modern French fête) "religious festival; noise, racket," from Vulgar Latin *festa (fem. singular; also source of Italian festa, Spanish fiesta), from Latin festa "holidays, feasts," noun use of neuter plural of festus "festive, joyful, merry," related to feriae "holiday" and fanum "temple," from PIE *dhes- "root of words in religious concepts" [Watkins]. The spelling -ea- was used in Middle English to represent the sound we mis-call "long e." Meaning "abundant meal" (whether public or private) is from late 14c.
feat (n.): mid-14c., "action, deeds," from Anglo-French fet, from Old French fait (12c.) "action, deed, achievement," from Latin factum "thing done," a noun based on the past participle of facere "make, do" (see factitious). Sense of "exceptional or noble deed" arose c.1400 from phrase feat of arms (French fait d'armes).
feather (n.): Old English feðer "feather," in plural, "wings," from Proto-Germanic *fethro (cf. Old Saxon fethara, Old Norse fioþr, Swedish fjäder, Middle Dutch vedere, Dutch veder, Old High German fedara, German Feder), from PIE *pet-ra-, from root *pet- "to rush, to fly" (see petition (n.)). Feather-headed "silly" is from 1640s. Feather duster attested by 1858. Figurative use of feather in (one's) cap attested by 1734.
feather (v.): Old English fiðerian "to furnish with feathers or wings," from feðer (see feather (n.)). Meaning "to fit (an arrow) with feathers" is from early 13c.; that of "to deck, adorn, or provide with plumage" is from late 15c. In reference to oars (later paddles, propellers, etc.) from 1740. Phrase feather one's nest "enrich oneself" is from 1580s. Related: Feathered; feathering.
feather-bed (n.): Old English feþerbedd; see feather (n.) + bed (n.).
featherweight: also feather-weight, the lightest allowable, 1812 (earlier as simply feather, 1760), from feather (n.) + weight. Originally in horse-racing; boxing use dates from 1889.
feature (n.): early 14c., "make, form, fashion," from Anglo-French feture, from Old French faiture "deed, action; fashion, shape, form; countenance," from Latin factura "a formation, a working," from past participle stem of facere "make, do, perform" (see factitious). Sense of "facial characteristic" is mid-14c.; that of "any distinctive part" first recorded 1690s. Entertainment sense is from 1801; in journalism by 1855. Meaning "a feature film" is from 1913.
feature (v.): 1755, "to resemble," from feature (n.). The sense of "make special display or attraction of" is 1888; entertainment sense from 1897. Related: Featured; featuring.
features (n.): "parts of the visible body" (especially the face), c.1300, from feature (n.).
febrifuge (n.): 1680s, from French fébrifuge, literally "driving fever away," from Latin febris (see fever) + fugare "to put to flight" (see fugitive).
febrile (adj.): 1650s, from Medieval Latin febrilis "pertaining to fever," from Latin febris "a fever" (see fever).
February (n.): late 14c., from Latin februarius mensis "month of purification," from februa "purifications, expiatory rites" (plural of februum), of unknown origin, said to be a Sabine word. The last month of the ancient (pre-450 B.C.E.) Roman calendar, so named in reference to the Roman feast of purification, held on the ides of the month. In Britain, replaced Old English solmonað "mud month." English first (c.1200) borrowed it from Old French Feverier, which yielded feoverel before a respelling to conform to Latin.
fecal (adj.): 1540s; see feces + -al (1).
feces (n.): also faeces, c.1400, "dregs," from Latin faeces "sediment, dregs," plural of faex (genitive faecis) "grounds, sediment, lees, dregs," of unknown origin. Specific sense of "human excrement" is from 1630s.
feckless (adj.): 1590s, from feck, "effect, value, vigor" (late 15c.), Scottish shortened form of effect, + -less. Popularized by Carlyle, who left its opposite, feckful, in dialectal obscurity. Related: Fecklessly; fecklessness.
feculent (adj.): late 15c., from Middle French féculent, from Latin faeculentus "abounding in dregs," from stem faec- (see feces). Related: Feculence.
fecund (adj.): early 15c., from Middle French fecond, from Latin fecundus "fruitful, fertile, productive," from *fe-kwondo-, suffixed form of Latin root *fe-, corresponding to PIE *dhe(i)- "to suck, suckle," also "produce, yield" (cf. Sanskrit dhayati "sucks," dhayah "nourishing;" Greek thele "mother's breast, nipple," thelys "female, fruitful;" Old Church Slavonic dojiti "to suckle," dojilica "nurse," deti "child;" Lithuanian dele "leech;" Old Prussian dadan "milk;" Gothic daddjan "to suckle;" Old Swedish dia "suckle;" Old High German tila "female breast;" Old Irish denaim "I suck," dinu "lamb").

Also from the same Latin root come felare "to suck;" femina "woman" (*fe-mna-, literally "she who suckles"); felix "happy, auspicious, fruitful;" fetus "offspring, pregnancy;" fenum "hay" (probably literally "produce"); and probably filia/filius "daughter/son," assimilated from *felios, originally "a suckling."
fecundity (n.): early 15c., from Latin fecunditatem (nominative fecunditas) "fruitfulness, fertility," from fecundus (see fecund).
fed (n.): 1788, short for Federalist; as colloquial for "official of the federal government," from 1916, especially, after 1930s, of FBI agents.
fed (adj.): past participle adjective from feed (v.). Fed up "surfeited, disgusted, bored," is British slang first recorded 1900, extended to U.S. by World War I; probably from earlier phrases like fed up to the back teeth.
fedayeen (n.): partisans or irregulars in the Middle East, from Arabic plural of fedai "devotee, zealot, one who risks life for a cause," from Persian fidai.
federal (adj.): 1640s, as a theological term, from French fédéral, from Latin foedus (genitive foederis) "covenant, league, treaty, alliance," related to fides "faith" (see faith).

Meaning "pertaining to a treaty" (1650s) led to political sense of "state formed by agreement among independent states" (1707), from phrases like federal union "union based on a treaty," popularized by formation of U.S.A. 1776-1787.
federalism (n.): 1793, American English, from French fédéralisme, from fédéral (see federal).
federalist (n.): "member or supporter of the Federal party in U.S. politics," originally of supporters of the Philadelphia constitution, 1787, American English, from federal + -ist. General sense of "one who supports federal union" is from 1792.
federate (v.): 1814 (implied in federated), back-formation from federation, or else from Latin foederatus "having a treaty, bound by treaty," past participle of foederare "to establish by treaty," from foedus (see federal). Related: Federating. As an adjective, by 1710.
federation (n.): 1721, "union by agreement," from French fédération, from Late Latin foederationem (nominative foederatio), noun of action from Latin foederare "league together," from foedus "covenant, league" (genitive foederis); see federal.
fedora (n.): 1887, American English, from "Fédora," a popular play by Victorien Sardou (1831-1908) that opened 1882, in which the heroine, a Russian princess named Fédora Romanoff, originally was performed by Sarah Bernhardt. During the play, Bernhardt, a notorious cross-dresser, wore a center-creased, soft brimmed hat. Women's-rights activists adopted the fashion. The proper name is Russian fem. of Fedor, from Greek Theodoros, literally "gift of god," from theos "god" + doron "gift" (see date (n.1)).
fee (n.): late 13c., from Old French fieu, fief "fief, possession, holding, domain; feudal duties, payment," from Medieval Latin feodum "land or other property whose use is granted in return for service," widely said to be from Frankish *fehu-od "payment-estate," or a similar Germanic compound, in which the first element is cognate with Old English feoh "money, movable property, cattle" (also German Vieh "cattle," Gothic faihu "money, fortune"), from PIE *peku- "cattle" (cf. Sanskrit pasu, Lithuanian pekus "cattle;" Latin pecu "cattle," pecunia "money, property"); second element similar to Old English ead "wealth."

OED rejects this, and suggests a simple adaptation of Germanic fehu, leaving the Medieval Latin -d- unexplained. Sense of "payment for services" first recorded late 14c. Fee-simple is "absolute ownership," as opposed to fee-tail "entailed ownership," inheritance limited to some particular class of heirs (second element from Old French taillir "to cut, to limit").
feeble (adj.): late 12c., from Old French feble (12c., Modern French faible) "weak, feeble," from Latin flebilis "lamentable," literally "that is to be wept over," from flere "weep, cry, shed tears, lament," from PIE *bhle- "to howl" (cf. bleat). The first -l- was dropped in Old French by dissimilation. The noun meaning "feeble person" is recorded from mid-14c.