The alternative is that it isn't matter at all, and that some other explanation is required for galactic rotation curves, the Bullet Galaxy, observed gravitational lensing, and the configuration of the cosmic microwave background.

It's nice that one theory currently does all of that. That doesn't guarantee that it's right, but it means it's more than just "we have a guess about one thing".

Dark implies the unknown. The Dark Ages weren’t literally dark, we just don’t have a lot of written sources from the era.

Transparent matter implies a known property about something we don’t know. To the extent dark matter is a problematic term, it’s in the matter but.

Even going with the first one, it's an incomplete description at best. "Dark" matter does not simply fail to emit light; it does not interact with light at all (other than by gravity, and that only bends it slightly, no absorption or emission involved).

Transparent fully captures this.

The overloaded meanings of those words which you are invoking are not relevant to the description of a physical property.

We don’t know this. We have a parcel of observations from which we are trying to intuit a cause.

1) We have unexplained observations.

2) A hypothetical explanation is dark matter, defined as a form of matter which does not interact with light (other than through gravity).

Whether dark matter actually exists does not affect how it's defined.

cause it's an assumption our "measurements" are representative of the reality of what's actually going on that far away.

we can't verify anything from this distance, so calling it empiricism is a stretch

We can’t directly sense most phenomena, and even then our senses can be misleading. Empiricism just means based on observation; that describes cosmology to a tee.