gentlewoman vs viscountess

gentlewoman

noun
  • A woman of the nobility. 

  • A female member of a legislature, especially a female member of a House of Representatives. 

viscountess

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

  • The wife of a viscount. 

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