at the drop of a hat 1. 一有信号(或激惹等)(就…) The dog responds at the drop of a hat. 那条狗一见到信号就作出反应。 2. 立即；毫不迟疑地；乐意地 He is willing to cancel the order at the drop of any hat. 他愿意随时取消定货。 She loves playing the piano and will give you a tune at the drop of a hat. 她爱弹琴，并乐意随时为您奏一曲。