khan vs overlord

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. 

overlord

noun
  • A ruler of other rulers. 

  • A feudal lord directly owed rent or personal service by a tenant of subinfeudated land, a tenant's liege lord. 

  • Anyone with overarching power or authority in a given domain. 

verb
  • To rule over; to domineer. 

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