execution vs mass murder

execution

noun
  • The act of putting to death or being put to death as a penalty, or actions so associated. 

  • The carrying out of an instruction, program or program segment by a computer. 

  • The act, manner or style of executing (actions, maneuvers, performances). 

  • The carrying into effect of a court judgment, or of a will. 

  • The formal process by which a contract is made valid and put into binding effect. 

  • The state of being accomplished. 

mass murder

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

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