Perhaps (as i mentioned before) or can be called merely a fundamental aspect of a world view, as in “an atheistic world view”.

I suppose I so tend to say “an atheistic world view” or “a theistic world view” when talking about the matter. That indicates more that it’s a fundamental characteristic of the world view, when compared to other world views, and not necessarily the world view itself.

By nature of the subject (gods being, in general, vast entities fundamental to the structure of the world), atheism is at least a fundamental aspect of an atheistic world view. That is, like magical unicorns, one couldn’t simply drop a god into an atheistic world view and have the people who hold that world view accept it without some serious issues.

I think being non-unicornian is also a fundamental facet of most atheistic world views.

Of course, ”non-unicornian" is a bit tongue-in-cheek. A somewhat better term might be “non-fantastical world views,” but whatever.