What came first, the atheist or the theist?

[Tiberius]

Which goes back to me questioning the OP. What exactly he meant.

I think Cecco made it quite clear with his wording:

"What came first, the atheist or the theist?"

Note the article "the" used before both atheist and theist. This indicates that the subject of the question is regarding actual atheists and theists, not the words, or even the concepts. If you expand the question by inserting the definitions for atheist and theist, the result is unambiguous:

"What came first, the person who didn't believe in God or the person who did?"

We've shown that people who don't believe things come before people who do, by the same logic that people who don't own cars come before people who do own cars.

Regardless, it isn't really important what the OP said, since the conversation has drifted in all sorts of directions to discuss the types of definition that can be used. What is important is how the discussion has evolved.