c. 1300, "characterized by vigor or strength; having qualities befitting a knight; valiant, hardy, courageous;" from Old French vertuos "righteous; potent; of good quality; mighty, valiant, brave" (12c.), from Late Latin virtuosus "good, virtuous," from Latin virtus "moral strength, high character, goodness; manliness; valor, bravery, courage (in war); excellence, worth," from vir "man" (from PIE root *wi-ro- "man").
From mid-14c. in English as "having beneficial or efficacious properties;" late 14c. (of persons) as "having excellent moral qualities; conforming to religious law." Related: Virtuously; virtuousness.