The word "up rear" is not commonly used in the English language, and therefore, it does not have a clear set of antonyms. However, if we consider the meanings of the individual words, "up" and "rear," some suitable antonyms can be identified. The opposite of "up" could be "down," "under," or "lower," while the antonyms for "rear" might be "front," "head," or "fore." Therefore, the antonyms for "up rear" can be a combination of these words, such as "downward front" or "lower fore." Despite the lack of a precise opposite for the term, the context can determine the most appropriate antonym for the situation.