deepen vs richen

deepen

verb
  • To become more sound or heavy. 

  • To make deep or deeper 

  • To make more sound or heavy. 

  • To become lower in tone 

  • To make darker or more intense; to darken 

  • To become deeper 

  • To become more intimate. 

  • To make lower in tone 

  • To become darker or more intense 

  • To become more thorough or extensive. 

  • To make more thorough or extensive. 

  • To make more intimate. 

  • To make more poignant or affecting; to increase in degree 

richen

verb
  • To gain richness; become heightened or intensified in brilliancy. 

  • To make or render rich or richer. 

  • To become rich or richer; become superior in quality, condition or effectiveness. 

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