duke vs oligarch

duke

noun
  • The sovereign of a small state. 

  • The male ruler of a duchy (female equivalent: duchess). 

  • A fist. 

  • A grand duke. 

  • A high title of nobility; the male holder of a dukedom. 

  • Any of various nymphalid butterflies of the Asian genera Bassarona and Dophla. 

verb
  • To hit or beat with the fists. 

  • To give cash to; to give a tip to. 

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. 

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