Proper term for someone who actively believes there is no god?

[Lehrling]

I pointedly ignored #3, as it doesn't really say what I am trying to say.

It does; you're just throwing the term "knowledge, not belief" around. Atheist means a lack of belief in god. Gnostic means a certainty of that belief. They are inherently related.

I respectfully disagree, although I get what you are trying to say. Atheism means a "lack" of belief in god (disbelief is not the anti-thesis of belief), and I am not "certain" in my disbelief, so it actually doesn't say what I'm trying to say.