allay vs heighten

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. 

heighten

verb
  • To make high; to raise higher; to elevate. 

  • To advance, increase, augment, make larger, more intense, stronger etc. 

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