I think this is one of those areas where the vast majority of people misuse certain terms, and that is partly due to misinformation and stigma attached to certain words.
I'm atheist and agnostic, there is no 'certainty', I call myself atheist for shorthand, but prefer the term 'de facto atheist' or 'agnostic atheist' when pressed on it. There is no evidence of a god, and ok, we cannot rule out god because we can't check under every rock, inside every teapot, and on top of every cloud to see if there is one sat there, but in all likelihood there isn't one or we would have some kind of evidence by now.
In my experience most 'agnostics' fall into this category. Most people think you can be only atheist or agnostic, and not both. Theists believe in one or more gods, atheists don't believe in the existence of gods.
Gnostics know with certainty, agnostics accept uncertainty.
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