allay vs lessen

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. 

lessen

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

  • To become less. 

conj
  • unless. 

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