Unpromise

Part of speech: verb

Definitions

1. To take back or withdraw a promise that was previously made
2. To retract or renege on a commitment one has given
3. To go back on a pledge or vow that was offered earlier

Etymology: "Unpromise" is a plain formation: the prefix "un-" joined to "promise," which keeps its ordinary sense of a pledge to do something. The reversal is spelled out in the word itself, meaning to withdraw or retract a promise already given, rather than to break one through neglect.