The word "unpromise" is a unique term that may sound unfamiliar to many. However, there are several synonyms that can convey a similar meaning. One such synonym is "revoke", which means to take back or cancel a promise. Another word that can be used interchangeably is "rescind", which implies the act of annulling or reversing a promise. Similarly, we can use the term "retract" as a synonym for "unpromise". This suggests the act of withdrawing or renouncing a previously made commitment. Overall, these synonyms provide alternative ways to express the concept of "unpromising" or retracting a pledge or agreement.