old lady vs surrogate mother

old lady

noun
  • One's mother. 

  • The Bank of England, sometimes referred to as the “Old Lady of Threadneedle Street” or simply “The Old Lady”. 

  • A queen. 

  • An elderly woman. 

  • One's girlfriend, wife or significant other. 

surrogate mother

noun
  • A woman who gives birth to a child not her own, with the intent to give that child up to at least one of the biological parents once it is born. 

How often have the words old lady and surrogate mother occurred in a corpus of books? (source: Google Ngram Viewer )