The antonyms for the phrase "carry to completion" can be words such as abandon, cease, fail, halt, leave, neglect, quit, stop or surrender. These antonyms signify the opposite of carrying an action to its completion level. Abandon implies leaving a task undone or discontinuing it halfway, whereas neglect means to ignore or disregard an obligation. Cease refers to stopping an action mid-way, while failing signifies being unsuccessful in accomplishing a task. Halting suggests bringing to an abrupt stop, and quitting means giving up on a task intentionally. Finally, surrender represents handing over or giving up on a task or struggle.