Bitterness, resentment, or any other negative emotion can be expressed in a variety of ways. RANCOUR (7 letters) is a French word meaning deep-seated and long-lasting bitterness or resentment. RANCOR (6 letters) is a synonym for RANCOUR, and is often used to describe a feeling of intense hatred or ill will. IRE (3 letters) is an old-fashioned term for anger or wrath. RANKLE (6 letters) is an informal word meaning to cause resentment or annoyance. ACRIMONY (8 letters) is a more formal word for bitterness or animosity. PIQUE (5 letters) is a feeling of irritation or resentment caused by a perceived slight or insult. Lastly, VENOM (5 letters) is a strong word for extreme hatred or malice.