The term "un-prolonged" means something that does not last for an extended period. Therefore, its antonyms can be terms that refer to things that endure for long periods. For example, the antonyms of un-prolonged include prolonged, prolonged-out, extended, stretched, and drawn-out. These words all indicate a state of continued existence or duration in time. In addition, other antonyms of un-prolonged can include "enduring," "long-lasting," "everlasting," "infinite," or "perpetual," all of which connote an uninterrupted or unremitting duration. Using these antonyms can help to convey the opposite meaning of "un-prolonged," making it easy to communicate more efficiently in writing and speaking.