Especially of poetry, drama, etc.: extempore, impromptu; improvised.
In early use not fully naturalized and frequently in Italian contexts..
Origin
Mid 18th century; earliest use found in Joseph Spence (1699–1768), literary scholar and anecdotist. From Italian improvviso, †improviso (of a composition in music, verse, or prose) extempore, specific sense development of improvviso (of a person) unprepared, (of a thing or event) unexpected, sudden from classical Latin imprōvīsus unforeseen, unexpected from im- + prōvīsus, past participle of prōvidēre.