acerbate vs importune

acerbate

verb
  • To exasperate; to irritate. 

  • To make bitter or sour. 

adj
  • Embittered; having a sour disposition or nature. 

importune

verb
  • To bother, irritate, trouble. 

  • To harass with persistent requests. 

  • To approach to offer one's services as a prostitute, or otherwise make improper proposals. 

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