noun
opponent's mistake; error by the enemy
Used in competitive contexts (sports, games, business, military) to refer to a mistake made by the opposing side that benefits one's own side.
試合は相手の敵失で勝った。
We won the match due to the opponent's mistake.
敵失を見逃さずに攻めるのが大事だ。
It's important to attack without overlooking the enemy's errors.