internecine vs slaughterous

internecine

adj
  • Mutually destructive; most often applied to warfare. 

  • Characterized by struggle within a group, usually applied to an ethnic or familial relationship. 

slaughterous

adj
  • prone to slaughtering 

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