dictator vs tetrarch

dictator

noun
  • A magistrate without colleague in republican Ancient Rome, who held full executive authority for a term granted by the senate (legislature), typically to conduct a war. 

  • A person who dictates text (e.g. letters to a clerk). 

  • A totalitarian leader of a country, nation, or government. 

  • A tyrannical boss or authority figure. 

tetrarch

noun
  • A governor or ruler of a quarter of a country, especially of a fourth part of a province in or client state of Ancient Rome. 

  • An officer in charge of a fourth part of a phalanx in Ancient Greece. 

  • Each of the four members of a jointly ruling tetrarchy, notably of the Roman Empire since Diocletian. 

How often have the words dictator and tetrarch occurred in a corpus of books? (source: Google Ngram Viewer )