KO vs coup de grâce

KO

verb
  • To knock someone out, to render someone unconscious. 

  • To start play. 

coup de grâce

noun
  • A final blow or shot given to kill a wounded person or animal. 

  • A remarkable finishing action. 

How often have the words KO and coup de grâce occurred in a corpus of books? (source: Google Ngram Viewer )