There are several synonyms for the phrase "lick promise" which means to make a promise that is empty or impossible to keep. One synonym for this phrase is "spitball promise" which derives from an English idiom that connotes making an assurance without backing it up. Another synonym for "lick promise" is "pie crust promise" which is like an easy to make pie crust that crumbles and breaks apart easily. A third synonym for this phrase is "bottle cap promise" which is an empty promise that holds no value or substance. Finally, "lip service promise" is a synonym that references the act of making an empty promise without any intention to follow through.