Ef'fi-ca-cy, n.

n. [Lat. efficacia, from efficax; Pr., Pg., & It. efficacia. Sp. eficacia, O. Fr. efficace, N. Fr. efficacité, from Lat. efficacitas.] Power to produce effects; production of the effect intended; as, the efficacy of medicine in counteracting disease; the efficacy of prayer. “Of noxious efficacy.” Milton.

Synonyms—Virtue; force; energy.