oligarchy vs tyranny

oligarchy

noun
  • A state ruled by such a government. 

  • Those who make up an oligarchic government. 

  • A government run by only a few, often the wealthy. 

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 oligarchy and tyranny occurred in a corpus of books? (source: Google Ngram Viewer )