- done without being planned, organized, or rehearsed临时的（地）, 即兴的（地）, 即席的（地）：
as adj. an impromptu press conference临时举行的记者招待会
as adv. he spoke impromptu.他即兴作了发言。
(pl. impromptus)
- a short piece of instrumental music, especially a solo, that is reminiscent of an improvisation即兴曲（尤指独奏）。
词源
mid 17th cent. (as an adverb)： from French， from Latin in promptu 'in readiness'， from promptus （see PROMPT）.