Drool
I'm not sure how exactly some people understand the word "religion", as in different from "belief", but I'd say that you for sure can apply at least one of them to the term "atheist" - in the practical sense.
1. Belief is something one BELIEVES, aka has NO "100% empirical proof" of.
Since you can't dis/prove G-d either way, at least if we're talking about G-d, that is BEYOND the physical world, - it boils down to a BELIEF, whether you believe in such a possibility or not.
It's made unprovable by the very definition I just mentioned.
2. Religion, on the other hand, is how one expresses that belief, in practical terms.
In this sense, at least when we're talking about the "aggressive" type of atheism (NOT so common here, thank G-d {
}), - atheists DO "preach" their RELIGION of FIGHTING the idea of G-d.
Still, those who do not actively address/harass others on that topic, by keeping it to themselves (or expressing it in the manner of OPINION, not ATTACK), would be harder to qualify as "religionists".
But in truth, even such people DO "have a religion".
It's being typically expressed in such "religiously obscure" actions like blind "belief" in SCIENCE, and even more so, in HUMANITY.
Yes, it starts as a mere belief (in some cases totally automatic/"normal" - thus NOT "religious"), but when people end up "worshiping" the HUMAN being (or rather, its accomplishments), we can end up with:
Double standards like racism (which was "based" on SCIENCE);
"Minority" promoting in the form of FIGHTING/DENYING the "normal" people (I'm not against PEOPLE which have such issues, I'm against when they call THAT being "normal", which is definitely NOT);
Corruption in justice and growing crime rates (based on the LACK of "religious" causes for NOT committing crimes; also the problem of SUBJECTIVE morality), which also ends up with perverting justice even in public (I mean, when it's OBVIOUS who's guilty);
Calling ALL human problems "natural" (I mean, these words are main ones to absolve anyone from behaving wrong/inHUMANe or discriminating others).