principality vs regnum

principality

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

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

regnum

noun
  • A rank in the classification of organisms, below dominium and above divisio. 

  • A badge of royalty, especially the early form of the pope's tiara. 

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