efficacious in WordNet English dictionary

1. 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"
   effective  effectual  efficacious 
   
2. 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"
   efficacious