Out-rivaling is the act of exceeding someone else's achievement or outdoing them in a particular task. However, there are antonyms for this term that signify the opposite or similar meanings. Some of the words that can be used as antonyms for out-rivaling include falling behind, trailing, lagging, underperforming, losing, and coming up short. When someone is falling behind, it means they are not performing or progressing as much as their peers or competitors. Trailings refer to being behind another person or group. Lagging means being slow or behind someone or something else. Underperforming refers to not meeting a particular expectation, while coming up short means missing or failing to meet a particular goal.