oligarch vs overlord

oligarch

noun
  • A member of an oligarchy; someone who is part of a small group that runs a country. 

  • A very wealthy business owner who wields political power. 

  • A protoplanet formed during oligarchic accretion. 

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