grand duchess vs grand duchy

grand duchess

noun
  • The wife or widow of a grand duke. 

  • A daughter or granddaughter of a sovereign (czar or later emperor) of the Russian Empire or a pretender to the throne thereof. 

  • The wife of a grand prince. 

grand duchy

noun
  • The territory owned, ruled, or reigned over by a grand duke or grand duchess; contrast grand dukedom. 

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