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"
the speech act of answering an attack on your assertions; "his refutation of the charges was short and persuasive"; "in defense he said the other man started it"
some situation or event that is thought about; "he kept drifting off the topic"; "he had been thinking about the subject for several years"; "it is a matter for the police"