coarsen vs harshen

coarsen

verb
  • To become (more) coarse. 

  • To make (more) coarse. 

harshen

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

  • To render peevish, morose, or austere. 

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