die out vs peter out

die out

verb
  • To become extinct. 

  • To cease gradually. 

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”) 

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