casern vs redoubt

casern

noun
  • A lodging for soldiers in a garrison town (formerly usually near the rampart); a barracks. 

redoubt

noun
  • A small, temporary, military fortification. 

  • A reinforced refuge; a fort. 

  • The return of doubt. 

  • A place of safety or refuge. 

verb
  • To fortify, to make into a stronghold. 

  • To doubt again. 

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