impromptu

adj.即席的；即兴的，临时的

adv.即兴地，无准备地

n.即兴之作；即兴曲

It usually take me more than three weeks to prepare a good impromptu speech. 为了准备一则即席的好讲辞，我通常要三个星期以上。

An impromptu visit broke up the long afternoon. 突然的造访打破了漫长的午后时光。

His call for a book of the trains had been a sheer piece of impromptu. 他打听火车时刻表只是一段纯粹的即兴曲。