reinforce vs richen

reinforce

verb
  • To strengthen, especially by addition or augmentation. 

  • To emphasize or review. 

  • To encourage (a behavior or idea) through repeated stimulus. 

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 reinforce and richen occurred in a corpus of books? (source: Google Ngram Viewer )