An agnostic disclaims any knowledge of God; an atheist denies the existence of God. That is, an agnostic says "I don't know whether there is a God"; the atheist says "There is no God." An agnostic does not deny the existence of a deity but claims that he does not know and that no one else can either. An atheist believes that God does not now exist and that He never has existed. Related terms are disbeliever, doubter, freethinker, unbeliever.
Dictionary of problem words and expressions. Harry Shaw. 1975.