benumb vs dullen

benumb

verb
  • To deaden, dull (the mind, faculties, etc.). 

  • To make numb, as by cold or anesthetic. 

dullen

verb
  • To become dull or duller; to dull. 

  • To make dull or duller; to dull. 

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