acerbate vs roil

acerbate

verb
  • To make bitter or sour. 

  • To exasperate; to irritate. 

adj
  • Embittered; having a sour disposition or nature. 

roil

verb
  • To annoy; to make angry; to throw into discord. 

  • To romp. 

  • To render turbid by stirring up the dregs or sediment of. 

  • To bubble, seethe. 

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