Efficacy
Pronunciation : Ef"fi*ca*cy
Part of Speech : n.
Etymology : [L. efficacia, fr. efficax. See Efficacious.]
Definition : Defn: Power to produce effects; operation or energy of an agent or force; production of the effect intended; as, the efficacy of medicine in counteracting disease; the efficacy of prayer. "Of noxious efficacy." Milton.
Syn. -- Virtue; force; energy; potency; efficiency.
Source : Webster's Unabridged Dictionary, 1913