The phrase "duty of loyalty" refers to the ethical obligation an individual has to act in the best interest of a person or organization they are affiliated with. Some synonyms include responsibility, obligation, commitment, fidelity, trust, and allegiance. These terms describe the sense of loyalty and commitment that is required in various relationships, such as a company and its employees, a government and its citizens, or a friend and their confidante. It is important for individuals to adhere to these principles of loyalty, as it helps to establish a sense of trust and reliability in any relationship. Without loyalty, relationships can quickly break down, causing harm and discord.