autocracy vs tyranny

autocracy

noun
  • A form of government in which unlimited power is held by a single individual. 

  • An instance of this government. 

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