on the fly   (TTS發音)

1. in flight在空中；在飛行中

    Tom was called out because the catcher caught the ball on the fly. 湯姆被判出局，因為接球員接住了飛來的球。

2. busy忙碌

    Getting the house ready for the visitors kept Mother on the fly all day. 為了把房子整理好接待客人，母親忙碌了一整天。

    The housekeeper of our school is always on the fly. 學校管理員整天忙得很。