General peace:
* Tranquility: A state of calmness and serenity.
* Harmony: A state of agreement and peaceful coexistence.
* Quiet: The absence of noise or disturbance.
* Calm: A state of being free from agitation or disturbance.
* Serenity: A state of being calm, peaceful, and untroubled.
Peace as a state of absence of conflict:
* Truce: A temporary suspension of hostilities.
* Ceasefire: A temporary stop in fighting.
* Conciliation: The act of bringing people together in a friendly way.
* Reconciliation: The act of restoring friendly relations.
Peace as a state of mind:
* Contentment: A state of happiness and satisfaction.
* Equanimity: A state of mental calmness, composure, and even temper, even in difficult situations.
* Composure: A state of calmness and control.
The best synonym for "peace" will depend on the specific context in which you are using it.