death knell vs death warrant

death knell

noun
  • A sign or omen foretelling the death or destruction of something. 

  • The tolling of a bell announcing death. 

death warrant

noun
  • That which definitively spells the end of something. 

  • An official warrant that authorizes capital punishment. 

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