enhance vs richen

enhance

verb
  • To augment or make something greater. 

  • To take up contrast agent (for an organ, tissue, or lesion). 

  • To improve something by adding features. 

  • To be raised up; to grow larger. 

richen

verb
  • To make or render rich or richer. 

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

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

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