acerbate vs mourn

acerbate

verb
  • To make bitter or sour. 

  • To exasperate; to irritate. 

adj
  • Embittered; having a sour disposition or nature. 

mourn

verb
  • To utter in a sorrowful manner. 

  • To express sadness or sorrow for; to grieve over (especially a death). 

  • To wear mourning. 

noun
  • Sorrow, grief. 

  • A ring fitted upon the head of a lance to prevent wounding an adversary in tilting. 

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