Online Etymology Dictionary

formidable (adj.): mid-15c., "causing fear," from Middle French formidable (15c.), from Latin formidabilis "causing fear, terrible," from formidare "to fear," from formido "fearfulness, fear, terror, dread." Sense has softened somewhat over time, in the direction of "so great (in strength, size, etc.) as to discourage effort." Related: Formidably.
formless (adj.): 1590s, from form (n.) + -less. Related: Formlessly; formlessness.
Formosa: old name of Taiwan, given by the Portuguese, from Portuguese Formosa insula "beautiful island." The adjective is from the fem. of Latin formosus "beautiful, handsome, finely formed," from forma "form, shape" (see form (n.)). Related: Formosan (1640s).
formula (n.): 1630s, "words used in a ceremony or ritual" (earlier as a Latin word in English), from Latin formula "form, draft, contract, regulation;" in law, "a rule, method;" literally "small form," diminutive of forma "form" (see form (n.)). Modern sense is colored by Carlyle's use (1837) of the word in a sense of "rule slavishly followed without understanding" [OED]. From 1706 as "a prescription, a recipe;" mathematical use is from 1796; chemistry sense is from 1842. In motor racing, "class or specification of a car" (usually by engine size), 1927.
formulae (n.): plural of formula.
Men who try to speak what they believe, are naked men fighting men quilted sevenfold in formulae. [Charles Kingsley, "Letters," 1861]
formulaic (adj.): 1845, from formula + -ic.
formular (n.): 1560s, "a model, exemplar," from Latin formula (see formula) + -ar. As an adjective, from 1773 as "formal, correct;" 1880 as "of or pertaining to a formula."
formulary (n.): 1540s, "collection of set forms," from French formulaire "collection of formulae," from noun use of Latin adjective formularius, from formula "a form" (see formula). As an adjective in English, "of the nature of a formula," 1728. The Latin adjective also was used as a noun meaning "a lawyer skilled in composing writs."
formulate (v.): "to express in a formula," 1837, from formula + -ate (2). Won out over formulize (1842); formularize (1845). Related: Formulated; formulating.
formulation (n.): 1848, noun of action from formulate (v.).
Fornax (n.): goddess of ovens in ancient Rome, from Latin fornax "furnace, oven, kiln" (see furnace). The dim constellation (representing a chemical furnace) was added by de Lacaille in 1756.
fornicate (v.): 1550s, "have illicit sexual intercourse" (said of an unmarried person), from Late Latin fornicatus, past participle of fornicari "to fornicate" (see fornication). Perhaps in some cases a back-formation from fornication. Related: Fornicated; fornicating.
fornication (n.): c. 1300, from Old French fornicacion "fornication, lewdness; prostitution; idolatry" (12c.), from Late Latin fornicationem (nominative fornicatio), noun of action from past participle stem of fornicari "to fornicate," from Latin fornix (genitive fornicis) "brothel" (Juvenal, Horace), originally "arch, vaulted chamber, a vaulted opening, a covered way," probably an extension, based on appearance, from a source akin to fornus "brick oven of arched or domed shape" (see furnace). Strictly, "voluntary sex between an unmarried man and an unmarried woman;" extended in the Bible to adultery. The sense extension in Latin is perhaps because Roman prostitutes commonly solicited from under the arches of certain buildings.
fornicator (n.): late 14c., from Late Latin fornicator, agent noun from fornicat-, stem of fornicari "to fornicate" (see fornication). Of the fem. forms, fornicatrice is c. 1500, fornicatrix 1580s, fornicatress 1590s.
fornix (n.): from 1680s in reference to various arched formations (especially in anatomy), from Latin fornix "arch, vaulted chamber, cellar, vaulted opening" (see fornication).
forsake (v.): Old English forsacan "object to, oppose, refuse, deny; give up, renounce" (past tense forsoc, past participle forsacen), from for- "completely" + sacan "to struggle, dispute, wrangle; accuse, blame" (see sake). Related: Forsaking. Similar formation in Old Saxon farsakan, Dutch verzaken, Old High German farsahhan "deny, repudiate," Danish forsage "give up, refuse."
Forsake is chiefly applied to leaving that by which natural affection or a sense of duty should or might have led us to remain: as, to forsake one's home, friends, country, or cause; a bird forsakes its nest. In the passive it often means left desolate, forlorn. [Century Dictionary]
forsaken (adj.): mid-13c., past participle adjective from forsake. Related: Forsakenly.
forsook: past tense of forsake.
forsooth (adv.): Old English forsoð "indeed, in truth, verily," from for-, perhaps here with intensive force (or else the whole might be "for a truth"), + soð "truth" (see sooth). Regarded as affected in speech by c. 1600.
forswear (v.): Old English forswerian "swear falsely" (intransitive), also "abandon or renounce on oath" (transitive), from for- "completely" + swerian "to swear" (see swear (v.)). Related: Forswore; forsworn; forswearing.
forsworn (adj.): from Old English forsworen, "perjured," past participle of forswerian "to swear falsely" (see forswear).
forsythia (n.): 1814, coined 1805 in Modern Latin as a genus name in honor of William Forsyth (1737-1804), Scottish horticulturalist who brought the shrub from China. The family name is from Gaelic Fearsithe "man of peace."
fort (n.): mid-15c., "fortified place, stronghold," from Old French fort "fort, fortress; strong man," noun use of adjective meaning "strong, stout, sturdy; hard, severe, difficult; hard to understand; dreadful, terrible; fortified" (10c.), from Latin fortis "strong, mighty; firm, steadfast; brave, spirited," from Old Latin forctus, possibly from PIE root *bhergh- (2) "high, elevated," with derivatives referring to hills and hill-forts (see barrow (n.2)). Or possibly from *dher- (2) "to hold firmly, support." Figurative use of hold the fort attested from 1590s.
Fort Sumter: military installation in South Carolina, U.S., begun in 1827, named for U.S. Revolutionary War officer and Congressman Thomas Sumter (1734-1832), "The Carolina Gamecock." The family name is attested from 1206, from Old French sommetier "driver of a pack horse" (see sumpter). The U.S. Civil War is held to have begun with the firing of rebel batteries on the government-held fort on April 12, 1861.
forte (n.): 1640s, fort, from French fort "strong point (of a sword blade)," from Middle French fort "fort, fortress" (see fort). Meaning "strong point of a person, that in which one excels," is from 1680s. Final -e- added 18c. in imitation of Italian forte "strong."
forte (adj.): music instruction, "loud, loudly," from Italian forte, literally "strong," from Latin fortis "strong" (see fort). Opposed to piano.
forth (adv.): Old English forð "forward, onward, further; continually;" as a preposition, "during," perfective of fore, from Proto-Germanic *furtha- "forward" (source also of Old Frisian, Old Saxon forth "forward, onward," Old Norse forð, Dutch voort, German fort), from extended form of PIE root *per- (1) "forward, through" (see per). The construction in and so forth was in Old English.
forthcoming (adj.): "about to happen or appear," late 15c., present participle adjective from Middle English forthcomen, from Old English forðcuman "to come forth, come to pass;" see forth + come (v.). Meaning "informative, responsive" is from 1835. A once-common verb formation; English also had forthbring, forthcall, forthdo, forthgo, forthpass, forthset, all now obsolete.
forthright (adj.): Old English forðriht "direct, plain;" see forth + right (adj.). Compare downright. Related: Forthrightly; forthrightness. As an adverb, Old English forðrihte "straightway, at once; plainly."
forthwith (prep.): c. 1200, from forth + with. The Old English equivalent was forð mid. As an adverb, early 14c.
forties (n.): 1843 as the years of someone's life between 40 and 49; from 1840 as the fifth decade of years in a given century. See forty. Also a designation applied in various places and times to certain oligarchies, ruling classes, or governing bodies.
It is well known that society in the island [Guernsey] is, or perhaps we ought to say, for many years was, divided into two sets, called respectively the Sixties and the Forties, the former composed of the old families and those allied to them, the latter of families of newly-acquired wealth and position. ["The Dublin Review," October 1877]
Roaring Forties are rough parts of the ocean between 40 and 50 degrees latitude.
fortieth (adj.): c. 1200, fowertiþe, from Old English feowertigoða, from feowertig (see forty) + -th (1). Compare Old Norse fertugonde, Swedish fyrationde, Danish fyrretyvende.
fortification (n.): early 15c., "a strengthening," also "defensive earthworks; a tower" (mid-15c.), from Old French fortification "strengthening, fortification," from Late Latin fortificationem (nominative fortificatio) "a strengthening, fortifying," noun of action from past participle stem of fortificare "to make strong" (see fortify).
fortify (v.): early 15c., "increase efficacy" (of medicine); mid-15c., "provide (a town) with walls and defenses," from Old French fortifiier (14c.) "to fortify, strengthen," from Late Latin fortificare "to strengthen, make strong," from Latin fortis "strong" (see fort) + facere "to make" (see factitious). Sense of "to strengthen mentally or morally" is from late 15c. Meaning "add liquor or alcohol" is from 1880; meaning "add nutrients to food" is from 1939. Related: Fortified; fortifying.
fortissimo (adj.): 1724, from Italian fortissimo, superlative of forte "loud, strong," from Latin fortis "strong" (see fort).
fortitude (n.): early 15c., from Middle French fortitude, from Latin fortitudo "strength, force, firmness, manliness," from fortis "strong, brave" (see fort).
fortitudinous (adj.): "capable of endurance," 1752, from Latin fortitudinem (nominative fortitudo) "strength, firmness" (see fortitude) + -ous. Related: Fortitudinously.
fortnight (n.): "period of two weeks," 17c. contraction of Middle English fourteniht, from Old English feowertyne niht, literally "fourteen nights," preserving the ancient Germanic custom of reckoning by nights (mentioned by Tacitus in "Germania" xi). Related: Fortnightly.
Fortran (n.): computer programming language, 1956, from combination of elements from formula + translation.
fortress (n.): early 14c., from Old French forteresse, forterece "strong place, fortification" (12c.), variant of fortelesse, from Medieval Latin fortalitia, from Latin fortis "strong" (see fort) + -itia, added to adjectives to form nouns of quality or condition. French -ess from Latin -itia also is in duress, largesse, riches. For change of medial -l- to -r- in Old French, compare orne "elm" from Latin ulmus; chartre from cartula; chapitre from capitulum.
fortuitous (adj.): 1650s, from Latin fortuitus "happening by chance, casual, accidental," from forte "by chance," ablative of fors "chance" (related to fortuna; see fortune). It means "accidental, undesigned" not "fortunate." Earlier in this sense was fortuit (late 14c.), from French. Related: Fortuitously; fortuitousness.
fortuity (n.): 1747, from stem of fortuitous + -ity.
fortunate (adj.): late 14c., "having good fortune; bringing good fortune," from Latin fortunatus "prospered, prosperous; lucky, happy," past participle of fortunare "to make prosperous," from fortuna (see fortune). Fortunate Islands "mythical abode of the blessed dead, in the Western Ocean" (early 15c.; late 14c. as Ilondes of fortune) translates Latin Fortunatae Insulae.
fortunately (adv.): "by (good) fortune," 1540s, from fortunate + -ly (2).
fortune (n.): c. 1300, "chance, luck as a force in human affairs," from Old French fortune "lot, good fortune, misfortune" (12c.), from Latin fortuna "chance, fate, good luck," from fors (genitive fortis) "chance, luck," possibly ultimately from PIE root *bher- (1) "to carry" (see infer). If so, the sense might be "that which is brought."

Sense of "owned wealth" is first found in Spenser; probably it evolved from senses of "one's condition or standing in life," hence "position as determined by wealth," then "wealth, large estate" itself. Often personified as a goddess; her wheel betokens vicissitude. Soldier of fortune first attested 1660s. Fortune 500 "most profitable American companies" is 1955, from the list published annually in "Fortune" magazine. Fortune-hunter "one who seeks to marry for wealth" is from 1680s.
fortune cookie (n.): by 1955, said to have been invented in 1918 by David Jung, Chinese immigrant to America who established Hong Kong Noodle Co., who handed out cookies that contained uplifting messages as a promotional gimmick.
fortune-teller (n.): also fortuneteller, 1580s, from fortune + teller. Verbal phrase tellen fortune is from early 15c.; verbal noun fortune-telling is by 1570s.
forty (n.): early 12c., feowerti, from Old English feowertig, Northumbrian feuortig "forty," from feower "four" (see four) + tig "group of ten" (see -ty (1)). Compare Old Saxon fiwartig, Old Frisian fiuwertich, Dutch veertig, Old High German fiorzug, German vierzig, Old Norse fjorir tigir, Gothic fidwor tigjus.
[T]he number 40 must have been used very frequently by Mesha's scribe as a round number. It is probably often used in that way in the Bible where it is remarkably frequent, esp. in reference to periods of days or years. ... How it came to be so used is not quite certain, but it may have originated, partly at any rate, in the idea that 40 years constituted a generation or the period at the end of which a man attains maturity, an idea common, it would seem, to the Greeks, the Israelites, and the Arabs. ["The International Standard Bible Encyclopedia," James Orr, ed., Chicago, 1915]
Forty winks "short sleep" is attested from 1821; in early use associated with, and perhaps coined by, English eccentric and lifestyle reformer William Kitchiner M.D. (1775-1827). Forty-niner in U.S. history was an adventurer to California (usually from one of the eastern states) in search of fortune during the gold rush of 1849.
forum (n.): mid-15c., "place of assembly in ancient Rome," from Latin forum "marketplace, open space, public place," apparently akin to foris, foras "out of doors, outside," from PIE root *dhwer- "door, doorway" (see door). Sense of "assembly, place for public discussion" first recorded 1680s.
forward (adv.): Old English forewearde "toward the front, in front; toward the future; at the beginning;" see fore + -ward. Adjectival sense of "early" is from 1520s; that of "presumptuous" is attested from 1560s. The Old English adjective meant "inclined to the front; early; former."