caliph vs commoner

caliph

noun
  • The political leader of the Muslim world; the successor of the prophet Muhammad's political authority. 

commoner

noun
  • A member of the common people who holds no title or rank. 

  • Someone who has a right over another's land. They hold common rights because of residence or land ownership in a particular manor, especially rights on common land. eg: centuries-old grazing rights 

  • Someone who is not of noble rank. 

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