I kind of like the term "error matter". It emphasizes that we're talking about error terms in the equations, yet admits that much of that error would be resolve

I kind of like the term "error matter". It emphasizes that we're talking about error terms in the equations, yet admits that much of that error would be resolved by the existence of matter. "Dark" is descriptive, but it requires that there actually be relatively normal matter involved, which is going forward an unwarranted step. And then it gets reused for "dark energy", which is... what, energy you can't see or interacts weakly with existing sensors? That's not novel or even unusual. The phrase is bogus. "Error energy" would work.