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late 15c., from Middle French effort, noun of action from Old French esforz "force, impetuosity, strength, power," back-formation 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. [Ortega y Gasset, 1949]Related: Efforts.