bivvy vs campground

bivvy

noun
  • A small tent or shelter. 

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

campground

noun
  • An area where tents are pitched. 

  • An area where a camp meeting (a retreat) is held. 

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