means Cruel, absolute, and unchecked power — rule by a single authority that answers to no one and serves only itself.

from From Greek 'tyrannos,' meaning an absolute ruler — though tellingly, the word itself isn't Greek in root. It seems to have been borrowed from somewhere in Asia Minor, possibly Lydian, which is why it has no good Greek etymology. In the earliest days a 'tyrannos' wasn't necessarily evil — just someone who seized power outside the usual royal succession, a strongman who grabbed the throne. Only over time, as Greeks soured on such rulers, did the word acquire its bitter taste, passing through Latin 'tyrannus' and Old French into English with all its menace intact.