The phrase "tie that binds" refers to something that brings people or things together. Synonyms for this phrase include commonality, connection, bond, attachment, and unity. A commonality suggests that people or things share a similarity or interest. A connection implies a relationship or association. A bond refers to a strong emotional or intellectual tie. An attachment implies a deep affection or loyalty. Unity suggests a sense of oneness or togetherness. All of these words convey a sense of connection or togetherness, and can be used interchangeably with "tie that binds" in most contexts. Whether in reference to people or things, these synonyms capture the essence of what brings them together.