Fort
late Middle English: from Old French fort or Italian forte, from Latin fortis ‘strong’.
wiktionary
From Middle English fort, from Middle French fort(“strong”) (adjective use is from Old French). Doublet of fortis and forte.
etymonline
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.
