Synonyms for Bitterness (same or very similar meaning)
WordNet sense 1 (a feeling of deep and bitter anger and ill-will):
gall, rancor, resentment, rancourWordNet sense 2 (the taste experience when quinine or coffee is taken into the mouth):
bitterWordNet sense 3 (a rough and bitter manner):
acerbity, acrimony, jaundice, tartness, thorninessFrom the ODE community, based on WordNetadd/edit