Undone might be considered as the antonym for "undoing." While undoing means the opposite of something, undone relates to something not being completed or finished. If one says something is undone, it implies that the work has not been entirely finished, or it can also suggest that the task is not yet accomplished. Various synonyms can be used for undone, including incomplete, unfinished, or unresolved. Oppositely, the word completion or accomplishment could be antonyms for the action of undoing. Therefore, undoing can be seen as the complete reversal of whatever has been done, whereas completing or accomplishing is the successful achievement of a task.