From Vulgar Latin *exfortiare (to force out) — 'ex-' + 'fortis' (strong). Literally a putting forth of strength.
A vigorous or determined attempt; the physical or mental energy needed to do something.
From Old French 'esfort' (exertion, force applied), from 'esforcier' (to force, to exert, to apply strength), from Vulgar Latin *exfortiāre (to put force outward), composed of 'ex-' (out, forth) + 'fortis' (strong, mighty, bold), from PIE *bʰerǵʰ- (high, elevated, great — the root of height and strength). The Latin 'fortis' (strong) gave English 'force,' 'fort' (a strong place), 'fortify' (to make strong), 'comfort' (strengthened together, hence 'con-fortare'), 'fortress,' 'fortitude' (moral strength), and 'effort' itself (strength pushed outward). PIE *bʰerǵʰ- also produced