field marshal vs potentate

field marshal

noun
  • In certain nations the highest military rank, ranking below only the commander in chief; now essentially disused. 

potentate

noun
  • A powerful leader; a monarch; a ruler. 

  • A self-important person. 

  • A powerful polity or institution. 

  • Someone acting in an important role. 

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