kingdom vs regnum

kingdom

noun
  • A rank in the classification of organisms, below domain and above phylum; a taxon at that rank (e.g. the plant kingdom, the animal kingdom). 

  • A realm, region, or conceptual space where something is dominant. 

  • A realm having a king and/or queen as its actual or nominal sovereign. 

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 kingdom and regnum occurred in a corpus of books? (source: Google Ngram Viewer )