oppress vs step on

oppress

verb
  • To make sad or gloomy. 

  • To keep down by unjust force. 

step on

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

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

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