Yes, I have noted that before.<quoted text>
You SHOULD note there was atheism before theism. Look in the derived terms and you will not see atheism.
156575; < Greek áthe ( os ) godless +-ist
158090; < Greek áthe ( os ) godless +-ism
The listing there doesn't list an origin date for: theism
Etymology online has a complete listing, too.
1630s, from atheist +-ic. Atheistical attested from c.1600.
1570s, from French athéiste (16c.), from Greek atheos "without god, denying the gods; abandoned of the gods; godless, ungodly," from a- "without" + theos "a god" (see Thea).
1580s, from French athéisme (16c.), from Greek atheos "without god" (see atheist). A slightly earlier form is represented by atheonism (1530s) which is perhaps from Italian atheo "atheist." Ancient Greek atheotes meant "ungodliness."
It means "without god", and more specifically, it means without a theistic belief, since theism is a belief.
The meaning of the root prefix, again.
a/n: not, without abyss without bottom; achromatic without color; anhydrous without water
The problem happens to be that words evolve along with our language, just as we do.
Many Dictionaries reflect the evolved meaning of the word.
A comprehensive look at what the word means in modern times, from the University of Cambridge.