empress vs king of kings

empress

noun
  • The female monarch (ruler) of an empire. 

  • The third trump or major arcana card of most tarot decks. 

  • A female chimpanzee. 

  • A deciduous tree, Paulownia tomentosa 

  • The wife or widow of an emperor or equated ruler. 

king of kings

noun
  • A king who has other kings as subjects; an emperor. 

name
  • Jesus Christ. 

  • The title of an individual king who has other kings as subjects; in particular 

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