bitterness vs reservations

bitterness

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

  • The quality of having a bitter taste. 

  • Harsh cold. 

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

reservations

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