backstair vs submerged

backstair

adj

  • clandestine, secret or furtive 

noun

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

submerged

adj

  • hidden 

  • underwater 

  • below the surface of a liquid 

  • poor, impoverished 

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