peter out vs weaken

peter out

verb
  • Synonym of peter (“originally (mining), of a vein of ore: to be depleted of ore; now (generally), to diminish to nothing; to dwindle, to trail off”) 

weaken

verb
  • To become weaker or less strong. 

  • To make weaker or less strong. 

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