The word "out-strip" refers to the process of surpassing or exceeding someone or something in terms of speed, performance, or achievement. However, there are several antonyms that represent the opposite of this term, including underperform, fall behind, lag, trail, and lose ground. Underperform refers to performing below one's expected level, while falling behind implies a trailing behind in terms of progress or advancement. Lag is a term used to describe moving at a slower pace than anticipated, while trailing refers to following behind someone or something. Lastly, losing ground implies a decline in performance or ranking. These antonyms provide a more comprehensive understanding of the concept of being outstripped.