This is not a tautology because it's not being used as a final explanation. It's called "matter" because the observational gaps appear to fit what would be some

This is not a tautology because it's not being used as a final explanation. It's called "matter" because the observational gaps appear to fit what would be some mass that we're missing and we think of matter as "stuff with mass". It's called "dark" because we can only observe it's gravitational impact and by all other observables, it doesn't show up. > Dark matter works well because it's designed to fill in the gaps in our current understanding of astrophysics data. "Works well" seems like you are looking at it the wrong way. Nobody is touting "dark matter" as a solution. It's the problem itself.