commoner vs viscount

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. 

viscount

noun
  • Any of various nymphalid butterflies of the genus Tanaecia. Other butterflies in this genus are called earls and counts. 

  • A member of the peerage, above a baron but below a count or earl. 

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