I can think of at least three different uses of the word atheist: one of which is from antiquity and is a pure accusation; one which is absurdly specific, so practically meaningless; and one which is nearly synonymous with a contemporary use of the word “Humanism”.
Atheism as a concept or body of ideas has a paradoxical aspect in that it only grows when religious hegemony intensifies. There are as many kinds of atheism as hegemonies from which people try to extract themselves. That is to say there is a Catholic atheism which is distinct from Islamic atheism which is distinct from Mormon atheism. Each shares a fundamental doubt of a cult’s claims, but that cult’s particular arrogation creates, in turn, a particular kind of seizing back of personal authority.