pentarchy vs tyranny

pentarchy

noun
  • A federation of five nations, each under its own government or ruler. 

  • Government by five persons. 

  • A governing body consisting of five persons. 

tyranny

noun
  • A government in which a single ruler (a tyrant) has absolute power; this system of government. 

  • The office or jurisdiction of an absolute ruler. 

  • Extreme severity or rigour. 

  • Absolute power, or its use. 

  • A system of government in which power is exercised on behalf of the ruler or ruling class, without regard to the wishes of the governed. 

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