* Vow: This is a strong and formal promise, often made in a religious or ceremonial context.
* Oath: This is a solemn promise made with a pledge to do something or to tell the truth, often with a penalty for breaking the oath.
* Pledge: This is a formal promise to do something, usually with a specific commitment or action attached.
* Covenant: This is a formal agreement between two or more parties, usually with legal or religious implications.
* Word of honor: This is a personal promise that is considered binding, even without a formal ceremony.
The best word to use will depend on the specific situation and the level of formality you need.