disburden vs mitigate

disburden

verb
  • To rid of a burden; to free from a load carried; to unload. 

  • To free from a source of mental trouble. 

mitigate

verb
  • To reduce, lessen, or decrease; to make less severe or easier to bear. 

  • To downplay. 

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