The word "prolongs" means to extend or lengthen the duration of something. Antonyms for "prolongs" include words like shorten, abbreviate, curtail and truncate. Shorten means to reduce the length or duration of something. Abbreviate refers to condensing or shortening something by omitting parts of it. Curtail means to cut short or bring to an abrupt end. Truncate refers to limiting or shortening the length of something by cutting or chopping off a part of it. These antonyms are especially useful when talking about time, where it is often necessary to communicate an action in a limited period.