That is exactly what atheism is. An atheist may believe in certain things, but whatever particular things a particular atheist believes in are not integral to atheism.
They are if they become so in standard usage of the term. So far, I am agreeing that technically atheism says something only about belief in god, but in common usage it is construed more broadly.
For instance, I'm a Buddhist. One should not generalize from that fact to say that atheism includes a belief in Buddhism.
One can, however, generalize from common usage of the term, which generally precludes not only belief in "gods" but also other supernatural forces or entities.
An atheist may be a materialist or may believe in astrology
Not in common usage. Atheism is not used to decribe people who don't believe in god but do believe in "faeries" or that our fate is determined by stellar constellations.
Absolutely not. Atheism is neither a system of theory nor a practice
1. I have already quoted from the oxford dictionary of etymology that "ism" is indeed used this way. Until you find a better given meaning of the suffix that fits this usage, you can't defend the above.
2. Plenty of dictionaries, from webster's to dictionary.com refer to atheism as a doctrine, which can and does mean "a body or system of beliefs or teachings."
3. Atheism comes from the greek word meaning godless or denying the gods, and the ism part goes back to french meaing a doctrine or system of belief wherein the gods or god is/are denied.
That changes nothing. The agnostic doesn't believe any theos exists, either.
An agnostic doesn't know. They don't believe a
theos exists, but they also don't believe that a
theos doesn't exist. They don't know. An atheist holds to a belief system in which NO theos exists. An agnostic doesn't. They don't know, or believe, one way or the other. An atheist does.
You have yet to show what the atheist "system of belief" is.
Technically, it is a system where the possibility of the reality or existence of supreme beings is systematically excluded. Agnostism, on the other hand, does not exclude, but does not include, either.
More commonly, the sytem excludes the possibility of any supernatural concepts, not just god.
Further, my belief that there is no god is not a dogmatic belief.
So what? No religion need be dogmatic or contrary to "revision." That does mean they aren't systems of belief.
Agnosticism, as defined above by Huxley, comes much closer to a system of belief than atheism.
I'm not denying that agnosticism is a system of belief. Simply that in that belief system the supernatural is neither included nor precluded, but an unknown.
The agnostic believes in the impenetrability of the mystery. The atheist is committed to no such dogmatic belief,
Wrong on both counts. Agnostics are not necessarily "dogmatically" or in any other way comitted to the impenetrability of the mystery. They can change their minds. They can be convinced that god does or does not exist. They need be no more or less dogmatic than atheists (who are frequently dogmatic).