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"
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"