imperator vs vizier

imperator

noun
  • An emperor. 

vizier

noun
  • vicegerent, viceroy 

  • A fairy chess piece that can only be moved one space up, down, left or right. 

  • An ancient Mesopotamian 𒈛 (sukkal). 

  • The highest-ranking official or minister in ancient Egypt or Ebla; a chief administrator or a chancellor. 

  • A high-ranking official or minister in an Islamic government, especially in the Ottoman Empire. 

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