duke vs queen mother

duke

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

  • A fist. 

  • A grand duke. 

  • The sovereign of a small state. 

  • 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. 

queen mother

noun
  • A widowed queen consort (a queen dowager) whose son or daughter from that marriage is the reigning monarch. 

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