bivvy vs garrison

bivvy

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

noun
  • A small tent or shelter. 

garrison

verb
  • To convert into a military fort. 

  • To occupy with troops. 

  • To assign troops to a military post. 

noun
  • The troops stationed at such a post. 

  • A permanent military post. 

  • Occupants. 

  • A military unit, nominally headed by a colonel, equivalent to a USAF support wing, or an army regiment. 

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