duchess vs viscountess

duchess

noun
  • The wife or widow of a duke. 

  • The female ruler of a duchy. 

verb
  • to court or curry favour for political or business advantage; to flatter obsequiously. 

viscountess

noun
  • The wife of a viscount. 

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

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