iˈfɛktʃuəl ɛf.ɪ.ˈkeɪ.ʃəs 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 effective teaching methods effective steps toward peace made an effective entrance his complaint proved to be effectual in bringing action an efficacious law marked by qualities giving the power to produce an intended effect written propaganda is less efficacious than the habits and prejudices … of the readers the medicine is efficacious in stopping a cough