Antonyms for "gains advantage" include "loses ground", "falls behind", "suffers loss", "misses out", "loses out", "backtracks", "falters", "retreats", "weakens", and "declines". These words denote the opposite of gaining an advantage, instead indicating a setback or underperformance. Losing ground suggests that progress has been made, but it has since been lost. Falling behind implies a failure to keep up with others. Suffering loss means that something valuable has been lost or taken away. Missing out indicates a missed opportunity, while losing out refers to being outdone or overshadowed by someone else. Backtracking or faltering denotes a failure to keep moving forward, while retreating suggests a retreat from a previously held position.