bitterness vs rancor

bitterness

noun
  • The quality of feeling bitter; acrimony, resentment; the quality of exhibiting such feelings. 

  • The quality of eliciting a bitter, humiliating or harsh feeling. 

  • The quality of having a bitter taste. 

  • Harsh cold. 

rancor

noun
  • A feeling of long-lasting ire for another, sometimes to the point of hatred, over a perceived wrongdoing; bitterness. 

  • Rancidity, rankness. 

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