Why not simply call it that, “the simple realization and acceptance that All is Self”? What do we need a one-word term for a simple realization? A one-word term is for complicated topics, not simple ones. Simple things can simply be described, they don’t need names. You need a convenient ‘name handle’ to describe a bundle of ideas that all go together. It sets the topic and the mood and announces that you’re dealing with a particular space.
One of those ideas in the bundle is that the self contains all. But there’s more to enlightenment than that.