Atheists don’t claim that there are no gods. It’s is impossible to prove the non-existence of something, so if you make such a claim, you get into belief territory. Most atheists are agnostic atheists, i.e. I’ll be happy to believe in your gods once you present evidence for their existence.

Fwiw, the “a-” prefix (see also “an-”, eg, “anhydrous”) can be described as “without”, “lack of”, or “not”.

Work out the definition for “theist” and go from there.

anti theists - there might be a god, but I don’t like him.