The term 'bitterly critical' can be broken down into three crossword solutions: RAIL (4 letters), RAILED (6 letters), and RUE (3 letters). RAIL is a verb meaning to criticize harshly or to scold. RAILED is the past tense of the verb, meaning to have criticized harshly or scolded. RUE is a verb meaning to regret or to feel sorrow for. Taken together, these words suggest that someone has expressed their criticism in a very harsh manner and now regrets it.