Most lengthened refers to something that has been extended to its greatest length or duration. Therefore, the antonyms or opposites of most lengthened can refer to something that is short, brief, or abbreviated. These words can include curt, succinct, brief, short, or concise. Another antonym of most lengthened can also be truncated, meaning to shorten, cut or curtail. These words represent the opposite of something that has been prolonged, extended or stretched out for a longer period of time. Overall, antonyms of most lengthened focus on the opposite of something that has been elongated or drawn out.