harshen vs tough

harshen

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

  • To render peevish, morose, or austere. 

tough

verb
  • To toughen. 

  • To endure. 

noun
  • A person who obtains things by force; a thug or bully. 

adj
  • Harsh or severe. 

  • Difficult or demanding. 

  • Stubborn or persistent; capable of stubbornness or persistence. 

  • Strong and resilient; sturdy. 

  • Undergoing plastic deformation before breaking. 

  • Difficult to cut or chew. 

  • Rugged or physically hardy. 

  • Rowdy or rough. 

intj
  • Used to indicate lack of sympathy 

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