[1] : The Collaborative International Dictionary of English v.0.48

efficacy \ef"ficacy\, n. l. efficacia, fr. efficax. see
   efficacious.
   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: efficacy.
        1913 webster

   syn: virtue; force; energy; potency; efficiency.
        1913 webster efficience
see also:
efficacious 

[2] : WordNet (r) 2.0

efficacy
     n : capacity or power to produce a desired effect; "concern
         about the safety and efficacy of the vaccine" syn: efficaciousness
         ant: inefficacy
see also:
efficaciousness inefficacy 

Efficacy >> E Words
Efficacy, definition of term: Efficacy
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