czar vs khan

czar

noun
  • An appointed official tasked to regulate or oversee a specific area. 

khan

noun
  • A ruler over various Turkish, Tatar and Mongol peoples in the Middle Ages. 

  • A noble or man of rank in various Muslim countries of Central Asia, including Afghanistan. 

  • A caravanserai; a resting-place for a travelling caravan. 

  • An Ottoman sultan. 

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