death knell vs knell

death knell

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

  • The tolling of a bell announcing death. 

knell

noun
  • A sign of the end or demise of something or someone. 

  • The sound of a bell knelling; a toll (particularly one signalling a death). 

verb
  • To ring a bell slowly, especially for a funeral; to toll. 

  • To signal or proclaim something (especially a death) by ringing a bell. 

  • To summon by, or as if by, ringing a bell. 

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