#1 bitterness n. [resentment, gall, rancor, rancour] a feeling of deep and bitter anger and ill-will. wn #2 bitterness n. [acrimony, acerbity, jaundice, tartness, thorniness] a rough and bitter manner. wn #3 bitterness n. [bitter] the taste experience when quinine or coffee is taken into the mouth. wn #4 bitterness n. [bitter] the property of having a harsh unpleasant taste. wn