viscount vs viscountess

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. 

viscountess

noun
  • A woman holding the rank of viscount in her own right. 

  • The wife of a viscount. 

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