acerbate vs unfriendly

acerbate

adj
  • Embittered; having a sour disposition or nature. 

verb
  • To exasperate; to irritate. 

  • To make bitter or sour. 

unfriendly

adj
  • Not friendly; hostile; mean. 

  • Unfavourable. 

noun
  • An enemy. 

adv
  • in an unkind or unfriendly manner; not as a friend 

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