on the fly 1. 在飞行中；未着地时 The bird caught a bug on the fly. 鸟在飞行中捉到一只虫子。 catch a ball on the fly 接住一个未落地的球 2. 〈口〉匆忙地；在忙碌之中；忙碌的 He had his breakfast on the fly. 他匆匆地吃早餐。 He can make decisions on the fly. 他能在匆忙中作出决定。 Housework keeps Mother on the fly all day. 家务劳动使母亲整天忙忙碌碌。 3. (计算机)运行中