The word "pro-longed" means ongoing or extended in duration. Antonyms for prolonged would be brief, fleeting, momentary, short-lived, transient or brief. The opposite of prolonged is something that does not continue for long, but instead occurs quickly or is brief. A brief event might not last for more than a few minutes, while a fleeting event may last only a few seconds. A momentary event is something that happens for an instant or a split-second, while a short-lived event lasts for a brief period of time. Transient refers to something that does not last long and is only temporary.