<p><strong>Adjective:</strong></p><ul><li>made or done without previous preparation: an impromptu address to the unexpected crowds.</li><li>suddenly or hastily prepared, made, etc.: an impromptu dinner.</li><li>improvised; having the character of an improvisation.</li></ul><p><strong>Noun:</strong></p><ul><li>something impromptu; an impromptu speech, musical composition, performance, etc.</li><li>a character piece for piano common in the 19th century and having, despite its title, a clear-cut form.</li></ul>