holocaust vs megadeath

holocaust

noun
  • Extensive destruction of a group of animals or (especially) people; a large-scale massacre or slaughter. 

  • Complete destruction by fire; also, the thing so destroyed. 

  • An offering or sacrifice to a deity that is completely burned to ashes. 

  • A complete or large offering or sacrifice. 

verb
  • To sacrifice (chiefly an animal) to be completely burned. 

  • To destroy (something) completely, especially by fire. 

  • To subject (a group of people) to a holocaust (mass annihilation); to destroy en masse. 

megadeath

noun
  • One million deaths, especially as a unit of measure in reference to nuclear warfare. 

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