Firbolgs (n.) Look up Firbolgs at Dictionary.com
1797, ancient supernatural people of Ireland (enemies of the Dannans), perhaps from Old Irish fir, plural of fear "man" + bolg, genitive plural of bolg "bag, belly;" or second element may be cognate with Gaulish Belgae.
fire (n.) Look up fire at Dictionary.com
Old English fyr, from Proto-Germanic *fuir (cognates: Old Saxon and Old Frisian fiur, Old Norse fürr, Middle Dutch and Dutch vuur, Old High German fiur, German Feuer), from PIE *perjos, from root *paewr- (cognates: Armenian hur "fire, torch," Czech pyr "hot ashes," Greek pyr, Umbrian pir, Sanskrit pu, Hittite pahhur "fire").

Current spelling is attested as early as 1200, but did not fully displace Middle English fier (preserved in fiery) until c.1600.

PIE apparently had two roots for fire: *paewr- and *egni- (source of Latin ignis). The former was "inanimate," referring to fire as a substance, and the latter was "animate," referring to it as a living force (see water (n.1)).

Fire applied in English to passions, feelings, from mid-14c. Meaning "action of guns, etc." is from 1580s. Firecracker is American English coinage for what is in England just cracker, but the U.S. word distinguishes it from the word meaning "biscuit." Fire-engine attested from 1680s. The figurative expression play with fire "risk disaster" is from 1887; phrase where's the fire? "what's the hurry?" first recorded 1924.
fire (v.) Look up fire at Dictionary.com
c.1200, furen, figurative, "arouse, excite;" literal sense of "set fire to" is from late 14c., from fire (n.). The Old English verb fyrian "to supply with fire" apparently did not survive into Middle English.

The sense of "sack, dismiss" is first recorded 1885 in American English (earlier "throw (someone) out" of some place, 1871), probably from a play on the two meanings of discharge: "to dismiss from a position," and "to fire a gun," fire in the second sense being from "set fire to gunpowder," attested from 1520s. Of bricks, pottery, etc., from 1660s. Related: Fired; firing. Fired up "angry" is from 1824. Firing squad is attested from 1904.
firearm (n.) Look up firearm at Dictionary.com
1640s, from fire (n.) + arm (n.2). Related: Firearms.
fireball (n.) Look up fireball at Dictionary.com
1550s, from fire (n.) + ball (n.1).
firebomb (n.) Look up firebomb at Dictionary.com
1895, from fire (n.) + bomb (n.). As a verb, from 1950 as an act of vandalism or terrorism, from 1941 as a military aviation tactic. Related: Firebombed; firebombing.
firebrand (n.) Look up firebrand at Dictionary.com
c.1200, "piece of wood kindled at a fire," from fire (n.) + brand (n.). Figurative sense of "one who kindles mischief or passions" is from late 14c.
firebug (n.) Look up firebug at Dictionary.com
"arsonist," 1872, from fire (n.) + bug (n.).
firefighter (n.) Look up firefighter at Dictionary.com
1903, from fire (n.) + fighter.
firefly (n.) Look up firefly at Dictionary.com
1650s, from fire (n.) + fly (n.).
firelight (n.) Look up firelight at Dictionary.com
Old English fyrleoht; see fire (n.) + light (n.).
fireman (n.) Look up fireman at Dictionary.com
late 14c., "tender of a fire," from fire (n.) + man (n.). As "person hired to put out (rather than tend) fires" it is attested from 1714.
fireplace (n.) Look up fireplace at Dictionary.com
c.1700, from fire (n.) + place (n.).
fireplug (n.) Look up fireplug at Dictionary.com
1713, from fire (n.) + plug (n.).
fireproof (adj.) Look up fireproof at Dictionary.com
1630s, from fire (n.) + proof. As a verb, from 1867. Related: Fireproofed; fireproofing.
fireside (n.) Look up fireside at Dictionary.com
1560s, from fire (n.) + side (n.). Symbolic of home life by 1848.
firewall (n.) Look up firewall at Dictionary.com
1851 as a physical wall meant to prevent the spread of fire in a structure, from fire (n.) + wall (n.). Computer sense is by 1990.
firewater (n.) Look up firewater at Dictionary.com
"alcoholic liquor," 1826, American English, supposedly from American Indians, from fire (n.) + water (n.1).
firewood (n.) Look up firewood at Dictionary.com
late 14c., from fire (n.) + wood (n.).
fireworks (n.) Look up fireworks at Dictionary.com
1570s, from fire (n.) + works (see work (n.)).
firkin (n.) Look up firkin at Dictionary.com
"small cask, fourth part of a barrel," late 14c., apparently from Middle Dutch *vierdekijn, diminutive of vierde, literally "fourth, fourth part" (see fourth).
firm (adj.) Look up firm at Dictionary.com
late 14c., from Old French ferm (12c.) "firm, strong, vigorous, steadfast; loyal, faithful," from Latin firmus "firm, strong, steadfast, enduring, stable," from PIE root *dher- (1) "to hold, support" (cognates: Sanskrit dharmah "custom, law," Greek thronos "seat," Lithuanian dirzmas "strong," Welsh dir "hard," Breton dir "steel"). The return in late 1500s to -i- from Middle English ferme was modeled on Latin. Related: Firmly; firmness.
firm (n.) Look up firm at Dictionary.com
"business house," 1744, from German Firma "a business, name of a business," originally "signature," from Italian firma "signature," from firmare "to sign," from Latin firmare "make firm, affirm," in Late Latin, "confirm (by signature)," from firmus "firm, stable" (see firm (adj.)).
firm (v.) Look up firm at Dictionary.com
c.1300, fermen "make firm, establish," from Old French fermer (12c.) or directly from Latin firmare, from firmus (see firm (adj.)). Related: Firmed; firming.
firmament (n.) Look up firmament at Dictionary.com
mid-13c., from Latin firmamentum "firmament," literally "a support or strengthening," from firmus "firm" (see firm (adj.)), used in Vulgate to translate Greek stereoma "firm or solid structure," which translated Hebrew raqia, a word used of both the vault of the sky and the floor of the earth in the Old Testament, probably literally "expanse," from raqa "to spread out," but in Syriac meaning "to make firm or solid," hence the erroneous translation.
firmware (n.) Look up firmware at Dictionary.com
1968, from firm (adj.) + ending from software.
firn (n.) Look up firn at Dictionary.com
"consolidated snow, the raw material of glaciers," 1853, literally "last year's snow, névé," from German Firn, from Swiss dialectal firn "of last year," from Middle High German virne "old," from Old High German firni, related to Old English fyrn "old," Gothic fairns "of last year," from Proto-Germanic *fur-/*for- (see first). The only English relic of a useful word meaning "of last year" that was widespread in Indo-European languages. It has cognates in Lithuanian pernai "last year," Greek perysi "a year ago, last year," Sanskrit parut "of last year."
first (adj., adv.) Look up first at Dictionary.com
Old English fyrst "foremost," superlative of fore; from Proto-Germanic *furisto- (cognates: Old Saxon fuirst "first," Old High German furist, Old Norse fyrstr, Danish første, Old Frisian ferist, Middle Dutch vorste "prince," Dutch vorst "first," German Fürst "prince"), superlative of *fur-/*for-, from PIE root *per- (1) "forward, through" (see per).

First-class (adj.) is from 1837; first-rate (1660s) is from classes of warships in the British navy. First aid is that given at the scene, pending the arrival of a doctor.

First Lady as an informal title for the wife of a U.S. president was in use by 1908, short for First lady of the land (by 1863 with reference to the president's wife). First name is attested from mid-13c.; first-born is from mid-14c. First base "a start" (1938) is a figurative use from the game of baseball.
firsthand (adj.) Look up firsthand at Dictionary.com
also first-hand, first hand, 1690s, from the image of the "first hand" as the source or origin of something.
firstly (adv.) Look up firstly at Dictionary.com
1530s, but never a common word (simple first usually serving its place), from first + -ly (2).
firth (n.) Look up firth at Dictionary.com
"arm of the sea, estuary of a river," early 15c., Scottish, from Old Norse fjörðr (see fjord).
fiscal (adj.) Look up fiscal at Dictionary.com
1560s, "pertaining to public revenue," from Middle French fiscal, from Late Latin fiscalis "of or belonging to the state treasury," from Latin fiscus "treasury," originally "purse, basket made of twigs (in which money was kept)," of unknown origin. The general sense of "financial" (1865, American English) was abstracted from phrases like fiscal calendar, fiscal year. Related: Fiscally.
fish (n.) Look up fish at Dictionary.com
Old English fisc, from Proto-Germanic *fiskaz (cognates: Old Saxon, Old Frisian, Old High German fisc, Old Norse fiskr, Middle Dutch visc, Dutch vis, German Fisch, Gothic fisks), from PIE *peisk- "fish" (cognates: Latin piscis, Irish iasc, and, via Latin, Italian pesce, French poisson, Spanish pez, Welsh pysgodyn, Breton pesk).

Fish story attested from 1819, from the tendency to exaggerate the size of the catch (or the one that got away). Figurative sense of fish out of water first recorded 1610s.
fish (v.) Look up fish at Dictionary.com
Old English fiscian (cognates: Old Norse fiska, Old High German fiscon, German fischen, Gothic fiskon), from the root of fish (n.). Related: Fished; fishing.
fish-hook Look up fish-hook at Dictionary.com
late 14c., from fish (n.) + hook (n.).
fisher (n.) Look up fisher at Dictionary.com
Old English fiscere, agent noun from fish (v.). It began to be used of certain animals, hence perhaps the rise of the formation fisherman (1520s).
fishery (n.) Look up fishery at Dictionary.com
"business of fishing," 1670s; "place where fish are caught," 1690s; see fish (v.) + -ery. Related: Fisheries.
fishing (n.) Look up fishing at Dictionary.com
verbal noun from fish (v.), c.1300, fysschynge; figurative use from 1540s. Fishing rod (1550s) is older than fishing pole (1791). To "go fishing" is as old as Old English on fiscoð gan.
[O]f all diversions which ingenuity ever devised for the relief of idleness, fishing is the worst qualified to amuse a man who is at once indolent and impatient. [Scott, "Waverly," 1814]
fishmonger (n.) Look up fishmonger at Dictionary.com
mid-15c., from fish (n.) + monger (n.).
fishtail (n.) Look up fishtail at Dictionary.com
1840, from fish (n.) + tail (n.). As a verb, 1927, originally of aircraft, later automobiles. Related: Fishtailed; fishtailing.
fishwife (n.) Look up fishwife at Dictionary.com
1520s, from fish (n.) + wife in the "woman" sense.
fishy (adj.) Look up fishy at Dictionary.com
late 15c., from fish (n.) + -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.) Look up fisk at Dictionary.com
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 (adj.) Look up fissile at Dictionary.com
1660s, from Latin fissilis "that which may be cleft or split," from fissus, past participle of findere (see fissure).
fission (n.) Look up fission at Dictionary.com
1841, "division of a cell or organism," from Latin fissionem (nominative fissio) "a breaking up, cleaving," from past participle stem of findere "to split" (see fissure). Cognate with Old English bitan "to bite." Nuclear physics sense is 1939. As a verb, from 1929.
fissure (n.) Look up fissure at Dictionary.com
c.1400, from Old French fissure (13c.) and directly from Latin fissura "a cleft," from root of findere "to split, cleave," from PIE *bhi-n-d-, from root *bheid- "to split" (cognates: Sanskrit bhinadmi "I cleave," Old High German bizzan "to bite," Old English bita "a piece bitten off, morsel," Old Norse beita "to hunt with dogs," beita "pasture, food").
fist (n.) Look up fist at Dictionary.com
Old English fyst, from West Germanic *fustiz (cognates: Old Saxon and Old High German fust, Old Frisian fest, Middle Dutch vuust, Dutch vuist, German Faust), from Proto-Germanic *fukhstiz, probably ultimately from PIE *penkwe- "five" (see five, and compare Old Church Slavonic pesti, Russian piasti "fist").
fistful (n.) Look up fistful at Dictionary.com
1610s, from fist (n.) + -ful.
fistic (adj.) Look up fistic at Dictionary.com
1806, from fist (n.) + -ic. Historically not considered proper English.
fisticuffs (n.) Look up fisticuffs at Dictionary.com
c.1600, from fist (n.) + cuff, perhaps in imitation of handiwork. Related: Fisticuff.