mass murder vs massacre

mass murder

noun
  • The killing of a large number of people over a short period of time. 

massacre

noun
  • The killing of a considerable number (usually limited to people) where little or no resistance can be made, with indiscriminate violence, without necessity, and contrary to civilized norms. 

  • St. Bartholomew's Day Massacre 

  • Any overwhelming defeat, as in a game or sport. 

verb
  • To win against (an opponent) very decisively. 

  • To perform (a work, such as a musical piece or a play) very poorly. 

  • To kill with great force or brutality. 

  • To kill in considerable numbers where little or no resistance can be made, with indiscriminate violence, without necessity, and contrary to civilized norms. (Often limited to the killing of human beings.) 

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