grand dukedom vs principality

grand dukedom

noun
  • The title of grand duke or grand duchess, with its pertaining privileges and obligations; contrast grand duchy. 

principality

noun
  • A region or sovereign nation headed by a prince or princess. 

  • A spiritual being, specifically in Christian angelology, the fifth level of angels, ranked above powers and below dominions. 

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