That's not the etymology or meaning of government though. It comes from "gubernare", latin which originally meant "to steer" or "to pilot". It entered english via Old French some 500-600 years ago.

Tyrant was adopted by the ancient greeks from another Eastern Mediterranean culture, and meant "sovereign ruler unlimited by law or constitution"; the notions of violence and actively terrorising people are later additions to the name, to the greeks it was simply a way to distinguish between a tyrant and the traditional kings and hereditary nobility.