duchy vs monarchy

duchy

noun
  • A dominion or region ruled by a duke or duchess. 

monarchy

noun
  • The territory ruled over by a monarch; a kingdom. 

  • A government in which sovereignty is embodied within a single, today usually hereditary head of state (whether as a figurehead or as a powerful ruler). 

  • States based on a system of governance headed by a king or a queen. 

  • A form of government where sovereignty is embodied by a single ruler in a state and his high aristocracy representing their separate divided lands within the state and their low aristocracy representing their separate divided fiefs. 

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