Efficacious

efficacious
    adj 1: marked by qualities giving the power to produce an
           intended effect; "written propaganda is less efficacious
           than the habits and prejudices...of the readers"-Aldous
           Huxley; "the medicine is efficacious in stopping a cough"
           [ant: {inefficacious}]
    2: producing or capable of producing an intended result or
       having a striking effect; "an air-cooled motor was more
       effective than a witch's broomstick for rapid long-distance
       transportation"-LewisMumford; "effective teaching methods";
       "effective steps toward peace"; "made an effective entrance";
       "his complaint proved to be effectual in bringing action";
       "an efficacious law" [syn: {effective}, {effectual},
       {efficacious}] [ant: {ineffective}, {ineffectual},
       {uneffective}]
    

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.
        [1913 Webster]
    

44 Moby Thesaurus words for "efficacious":
      able, active, adequate, authoritative, capable, charismatic,
      charming, competent, consequential, effective, effectual,
      efficient, enchanting, equal to, estimable, functional, go,
      important, influential, magnetic, momentous, operational,
      operative, personable, persuasive, potent, powerful, practical,
      prestigious, productive, proficient, puissant, reputable,
      serviceable, strong, suasive, substantial, successful, telling,
      up to, useful, virtuous, weighty, winning