bivouac vs bivy

bivouac

verb
  • To set up camp. 

  • To encamp for the night without tents or covering. 

  • To watch at night or be on guard, as a whole army. 

noun
  • An encampment for the night, usually without tents or covering. 

  • Any temporary encampment. 

  • A temporary shelter constructed generally for a few nights. 

  • A structure formed by migratory ants out of their own bodies to protect the queen and larvae. 

bivy

verb
  • To camp in a bivouac. 

noun
  • A bivouac sack. 

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