"Lick a promise" is a colloquial phrase that means to make a promise with a gesture of confidence or certainty. There are several synonyms that can be used in place of "lick a promise" to convey the same idea, such as "swear by," "vow," "pledge," "commit," "guarantee," and "assure." Each of these terms suggests a level of conviction and certainty in the promise being made. For instance, when someone swears by something, they're essentially putting their reputation and credibility on the line, so it's a strong indication that they're confident in their ability to deliver on their promise. Overall, the concept of making a promise with a gesture of confidence is a common expression in many cultures and languages.