emperor vs khan

emperor

noun
  • The male monarch or ruler of an empire. 

  • A large, relatively valuable marble in children's games. 

  • Any of various butterflies of the subfamily Charaxinae. 

  • Specifically, the ruler of the Holy Roman Empire; the world-monarch. 

  • Any of various large dragonflies of the cosmopolitan genus Anax. 

  • An emperor penguin. 

  • The fourth trump or major arcana card of the tarot deck. 

  • Any monarch ruling an empire, irrespective of gender, with "empress" contrasting to mean the consort of an emperor. 

  • Any fish of the family Lethrinidae. 

khan

noun
  • An Ottoman sultan. 

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

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

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

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