befog vs blur

befog

verb
  • To confuse, mystify (a person); to make less acute or perceptive, to cloud (a person’s faculties). 

  • To envelop in fog or smoke. 

  • To obscure, make less clear (a subject, issue, etc.). 

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 

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