potentate vs rex

potentate

noun
  • A self-important person. 

  • A powerful leader; a monarch; a ruler. 

  • A powerful polity or institution. 

  • Someone acting in an important role. 

rex

noun
  • An animal which has a genetic recessive variation that causes the guard hairs to be very short or fully lacking. 

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