duchy vs kingship

duchy

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

kingship

noun
  • The territory or dominion of a king; a kingdom. 

  • A monarchy. 

  • The dignity, rank or office of a king; the state of being a king. 

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