harshen vs hebetate

harshen

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

  • To render peevish, morose, or austere. 

hebetate

verb
  • To render obtuse; to dull; to blunt. 

adj
  • obtuse; dull 

  • Having a dull or blunt and soft point 

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