allay vs mitigate

allay

verb
  • To alleviate; to abate; to mitigate. 

  • To make quiet or put at rest; to pacify or appease; to quell; to calm. 

noun
  • Alleviation; abatement; check. 

mitigate

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

  • To downplay. 

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