Hi, an agnostic here ... just agnostic.

[Jesster]

Yes you can. You do so by piecing together the word parts. Please learn how to Greek.

Rofl. "Atheos" is the root word of both "atheist" and "atheism", with suffix swaps. "Theist" isn't the root for "atheist" and "theism" the root for "atheism". 

John Kersey the younger, A New English Dictionary (1702)
Atheism, the Opinion of
An Atheist, who denies the Being of a God.

An Universal Etymological English Dictionary, Nathan Bailey, R. Ware, 1756
ATHEIST (from Gr. without God) one that denies the exiftence of God.

A dictionary of the English language., Samuel Johnson, 1768
A’the-ist, f. One that denies the existence of a God.

“ATHEISM and atheist are words formed from Greek roots and with Greek derivative endings. Nevertheless they are not Greek ; their formation is not consonant with Greek usage. In Greek they said atheos and atheotes ; to these the English words ungodly and ungodliness correspond rather closely. In exactly the same way as ungodly, atheos was used as an expression of severe censure and moral condemnation ; this use is an old one, and the oldest that can be traced. Not till later do we find it employed to denote a certain philosophical creed ; we even meet with philosophers bearing atheos as a regular surname. We know very little of the men in question ; but it can hardly be doubted that atheos, as applied to them, implied not only a denial of the gods of popular belief, but a denial of gods in the widest sense of the word, or Atheism as it is nowadays understood.”, Atheism in pagan antiquity by Drachmann, A. B.

Rofl, you're boring me. Now you're just restating what others have said when I don't care about their authority. I don't care at all about personal usage. None of that has anything to do with the word structure. "A-" is a prefix to "theos" no matter how many times you try to deny it. "The" is the shortened form of "theos" used in "theism" and "a-" is the prefix. Look it the fuck up. I'm tired of this coming down to an assertion-fest.

I'll let the others get back to welcoming you now.