disburden vs lessen

disburden

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

  • To free from a source of mental trouble. 

lessen

verb
  • To make less; to diminish; to reduce. 

  • To become less. 

conj
  • unless. 

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