bivvy vs dormitory

bivvy

noun
  • A small tent or shelter. 

verb
  • To erect, or to stay in, such a tent or shelter. 

dormitory

noun
  • A room containing a number of beds (and often some other furniture and/or utilities) for sleeping, often applied to student and backpacker accommodation of this kind. 

  • A building or part of a building which houses students, soldiers, monks etc. who sleep there and use communal further facilities. 

  • A dormitory town. 

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