peer of the realm vs viscount

peer of the realm

noun
  • Any similar member of the nobility of other kingdoms. 

  • Any member of the hereditary peerage of the United Kingdom, (chiefly) of the Kingdom of England. 

  • Any member of the House of Lords who is not a life peer. 

viscount

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

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

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