step on vs stomp on

step on

verb
  • to adulterate a drug for the purpose of increasing its bulk, and therefore its profit; to dilute, cut. 

  • Used other than figuratively or idiomatically: see step, on. 

stomp on

verb
  • to severely mistreat 

  • to severely defeat. 

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