soften vs weaken

soften

verb
  • To become soft or softer 

  • To make something soft or softer. 

  • To palatalize. 

  • To become or make (a consonant) more lenis, to lenite. 

  • To make less harsh 

  • To undermine the morale of someone (often soften up). 

weaken

verb
  • To make weaker or less strong. 

  • To become weaker or less strong. 

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