grand vizier vs overlord

grand vizier

noun
  • A figure of great authority and power. 

  • The greatest minister of a sultan, with absolute power of attorney and, in principle, dismissable only by the sultan himself. 

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 grand vizier and overlord occurred in a corpus of books? (source: Google Ngram Viewer )