dullen vs dwindle

dullen

verb
  • To become dull or duller; to dull. 

  • To make dull or duller; to dull. 

dwindle

verb
  • To lessen; to bring low. 

  • To decrease, shrink, diminish, reduce in size or intensity. 

  • To break up or disperse. 

  • To fall away in quality; degenerate, sink. 

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