Etymologically the word obvious comes from ob + via, in other words something blocking the path (to understanding). But in modern usage it's of course used to mean the opposite, something that's trivially easy to see. Though ironically most propositions prefaced by 'obviously' are anything but.

Anyway, if no such word exists, I'd propose propose calling them obvianyms, after what is perhaps the best-known example of the phenomenon. Plus, the fact that the term is actually an anti-cognate adds a third layer of irony, which is kind of cool in and of itself.