grim vs harshen

grim

verb
  • To make grim; to give a stern or forbidding aspect to. 

adj
  • Rigid and unrelenting. 

  • Ghastly or sinister. 

  • Disgusting; gross. 

  • Dismal and gloomy, cold and forbidding. 

harshen

verb
  • To make, or to become harsh; render hard and rough. 

  • To render peevish, morose, or austere. 

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