Probably from the latin arcus, meaning "arch" or "bow." I don't think it has a specific intended meaning in this case, but is more used to imply a technological/archaic/arcane connection; that is, this person is not only a flagellant, but they are a mechanized super-flagellant.
That said, this is all idle theorizing, not based in fact.
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!