Ackshully, "galaxy" (or rather, "galaxias") means "Milky Way" already, it's just a translation. It was less ambiguous when the only galaxy we could see was the Milky lights that covered a lot of our sky.
Of course, we realize there's more than one galaxy now, so the meanings have diverged.
It can mean mean any sort of extra-judicial punishment. I agree it's not the best choice of words, but context makes it pretty clear that he was not killed.