matron vs viscountess

matron

noun
  • A female prison officer. 

  • A mature or elderly woman. 

  • A woman of staid or motherly manners. 

  • A wife or a widow, especially, one who has borne children. 

  • A housekeeper, especially, a woman who manages the domestic economy of a public institution. 

  • A senior female nurse in an establishment, especially a hospital or school. 

viscountess

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

  • The wife of a viscount. 

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