Pronunciation: (im-promp'tOO, -tyOO),[key] —adj. 1. made or done without previous preparation: an impromptu address to the unexpected crowds. 2. suddenly or hastily prepared, made, etc.: an impromptu dinner. 3. improvised; having the character of an improvisation.
—adv. without preparation: verses written impromptu.
—n. 1. something impromptu; an impromptu speech, musical composition, performance, etc.
2. a character piece for piano common in the 19th century and having, despite its title, a clear-cut form.