duchy vs republic

duchy

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

republic

noun
  • A state where sovereignty rests with the people or their representatives, rather than with a monarch or emperor; a country with no monarchy. 

  • One of the subdivisions constituting Russia. See oblast. 

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