blur vs dullen

blur

verb
  • To make indistinct or hazy, to obscure or dim. 

  • To cause imperfection of vision in; to dim; to darken. 

  • To become indistinct. 

  • To transfer the input focus away from. 

  • To smear, stain or smudge. 

adj
  • In a state of doubt or confusion. 

noun
  • Something that appears hazy or indistinct 

  • A smear, smudge or blot 

dullen

verb
  • To make dull or duller; to dull. 

  • To become dull or duller; to dull. 

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