How can a overarching concept of the divine actually be defined as nothing? 'Divine' does have some content and some definition, doesn't it? If it doesn't, then why are you even discussing a word that has no definition? This is not analogous to 'humanity', that has a much more succinct definition and, no, cannot and does not mean 'nothing', 'anything', nor 'everything'.
I don't think you should be stating it as divine having no 'known' characteristics; again, we're addressing claims and propositions, whether we conclude that there is any actual knowledge supporting or not supporting those claims is a separate issue. Theists make claims, and those claims are not that the divine is nothing.
Every definition I can find refers to atheism being the disbelief in gods or supreme beings, not just a nebulous entirely undefined 'divine'; maybe we're not even agreeing on what atheism actually is since I think you think it is the rejection of the undefined 'divine', when atheism is apparently narrower than that, since the divine can mean anything. As I said before, it's pretty hard to assent or dissent from something that has no definition. And I find 'can be anything, everything , or nothing' to be equivalent to having no definition.