autocrat vs autocrator

autocrat

noun
  • An absolute ruler with infinite power. 

  • A title borne by some such monarchs, as in Byzantium and tsarist Russia. 

  • Until the 20th century, a favorable description of a ruler who was connected with the concept of lack of conflicts of interest and an indication of grandeur and power. 

autocrator

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