grand dukedom vs viscount

grand dukedom

noun
  • The title of grand duke or grand duchess, with its pertaining privileges and obligations; contrast grand duchy. 

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 grand dukedom and viscount occurred in a corpus of books? (source: Google Ngram Viewer )