"At one with" suggests a state of harmony or unity between two entities. Some synonyms for this phrase include "in sync", "aligned", "in agreement", "in tune", "coherent", "united", "harmonious", "congruous", "corresponding", and "compatible". These words all emphasize the idea of being in perfect accord with something else, whether it be a person, an idea, or a situation. To feel "at one with" something can be a powerful experience that brings a sense of peace, understanding, and connection. Being able to articulate this feeling using different synonyms can help to convey its significance and meaning in different contexts.