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"
not suspected or believed likely; "remained unsuspected as the head of the spy ring"; "he was able to get into the building unspotted and unsuspected"; "unsuspected difficulties arose"; "unsuspected turnings in the road"