Etymology
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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, which is of unknown etymology. Possibly from PIE root *bhergh- (2) "high, elevated," with derivatives referring to hills and hill-forts, or possibly from *dher- "to hold firmly, support." Figurative use of hold the fort attested from 1590s.

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fortissimo (adj.)
1724, from Italian fortissimo, superlative of forte "loud, strong," from Latin fortis "strong" (see fort).
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forte (adj.)
music instruction, "loud, loudly," from Italian forte, literally "strong," from Latin fortis "strong" (see fort). Opposed to piano.
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fortitude (n.)

late 14c., "moral strength (as a cardinal virtue); courage," from Latin fortitudo "strength, force, firmness, manliness," from fortis "strong, brave" (see fort). From early 15c. as "physical strength."

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forte (n.)

1640s, fort, from French fort "strong point (of a sword blade)," earlier "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."

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aqua fortis (n.)
also aquafortis, old commercial name for "diluted nitric acid," c. 1600, Latin, literally "strong water;" see aqua- + fort. So called for its power of dissolving metals (copper, silver) which are unaffected by other agents.
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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.
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comfort (v.)

late 13c., conforten "to cheer up, console, soothe when in grief or trouble," from Old French conforter "to comfort, to solace; to help, strengthen," from Late Latin confortare "to strengthen much" (used in Vulgate), from assimilated form of Latin com-, here perhaps an intensive prefix (see com-), + fortis "strong" (see fort).

The change of -n- to -m- began in English 14c. In Middle English also "give or add strength to" (c. 1300); "encourage, urge, exhort" (c. 1300). Related: Comforted; comforting.

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force (n.)
c. 1300, "physical strength," from Old French force "force, strength; courage, fortitude; violence, power, compulsion" (12c.), from Vulgar Latin *fortia (source also of Old Spanish forzo, Spanish fuerza, Italian forza), noun use of neuter plural of Latin fortis "strong, mighty; firm, steadfast; brave, bold" (see fort).

Meanings "power to convince the mind" and "power exerted against will or consent" are from mid-14c. Meaning "body of armed men, a military organization" first recorded late 14c. (also in Old French). Physics sense is from 1660s; force field attested by 1920. Related: Forces.
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effort (n.)

late 15c., "laborious attempt, strenuous exertion," from French effort, from Old French esforz "force, impetuosity, strength, power," verbal noun from esforcier "force out, exert oneself," from Vulgar Latin *exfortiare "to show strength" (source of Italian sforza), from Latin ex "out" (see ex-) + Latin fortis "strong" (see fort).

Effort is only effort when it begins to hurt. [José Ortega y Gasset, writing of Goethe in Partisan Review, vol. xvi, part ii, 1949]

Related: Efforts "voluntary exertion," also "result of exertion."

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