khan vs ruler

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. 

ruler

noun
  • A person who rules or governs; someone or something that exercises dominion or controlling power over others. 

  • A (usually rigid), flat, rectangular measuring or drawing device with graduations in units of measurement; a straightedge with markings. 

verb
  • To beat with a ruler (as a traditional school punishment). 

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