- efficacy
- 1520s, from L. efficacia, from efficax (gen. efficacis) "effective," from efficere "work out, accomplish" (see effect).
- efficacious
- 1520s, from L. efficaci- (see efficacy).
- inefficacy
- "want of force or virtue to produce the desired effect," 1612, from L.L. inefficacia, from inefficacem (nom. inefficax), from in- "not" + efficax (see efficacy).
- virtual
- late 14c., "influencing by physical virtues or capabilities," from M.L. virtualis, from L. virtus "excellence, potency, efficacy," lit. "manliness, manhood" (see virtue). The meaning of "being something in essence or fact, though not in name" is first recorded 1650s, probably via sense of "capable of producing a certain effect" (early 15c.). Computer sense of "not physically existing but made to appear by software" is attested from 1959. Virtually (early 15c.) originally meant "as far as essential qualities or facts are concerned;" sense of "in effect, as good as" is recorded from c.1600.
- virtue
- early 13c., "moral life and conduct, moral excellence," vertu, from Anglo-Fr. and O.Fr. vertu, from L. virtutem (nom. virtus) "moral strength, manliness, valor, excellence, worth," from vir "man" (see virile). Phrase by virtue of (early 13c.) preserves alternative M.E. sense of "efficacy." Wyclif Bible has virtue where K.J.V. uses power. The seven cardinal virtues (early 14c.) were divided into the natural (justice, prudence, temperance, fortitude) and the theological (hope, faith, charity). To make a virtue of a necessity (late 14c.) translates L. facere de necessitate virtutem. [Jerome]