cool off vs soften

cool off

verb
  • To decrease in temperature, activity, or temper. 

  • To cause to decrease in temperature, activity or temper. 

soften

verb
  • To make less harsh 

  • To make something soft or softer. 

  • To palatalize. 

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

  • To become soft or softer 

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

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