Source : Webster's Revised Unabridged Dictionary (1913)

Efficacious \Ef`fi*ca"cious\, a. [L. eficax, -acis, fr.
   efficere. See {Effect}, n.]
   Possessing the quality of being effective; productive of, or
   powerful to produce, the effect intended; as, an efficacious
   law.

   Syn: See {Effectual}. -- {Ef`fi*ca"cious*ly}, adv. --
        {Ef`fi*ca"cious*ness}, n.

Source : WordNet®

efficaciously
     adv : in an effective manner; "these are real problems that can be
           dealt with most effectively by rational discussion"
           [syn: {effectively}] [ant: {inefficaciously}, {inefficaciously}]