backstair vs harborage

backstair

noun
  • The backstairs (stairs at the rear of a building). 

adj
  • clandestine, secret or furtive 

harborage

noun
  • A place of shelter or entertainment. 

  • A condition on land favorable to infestation by animals considered pests. 

  • A place for refuge for a vessel. 

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