dictator (n.)

late 14c., dictatour, "Roman chief magistrate with absolute authority," from Old French dictator and directly from Latin dictator, agent noun from dictare "say often, prescribe," frequentative of dicere "to say, speak" (from PIE root *deik- "to show," also "pronounce solemnly").

In Latin, a dictator was a judge in the Roman republic temporarily invested with absolute power; this historical sense was the original one in English. The transferred sense of "absolute ruler, person possessing unlimited powers of government" is from c. 1600; that of "one who has absolute power or authority" of any kind, in any sphere is from 1590s.