1808, from Italian improvisare "to sing or speak extempore," from Latin improviso "unforeseen; not studied or prepared beforehand," ablative of improvisus "not foreseen, unexpected," from assimilated form of in- "not, opposite of" (see in- (1)) + provisus "foreseen," also "provided," past participle of providere "foresee, provide" (see provide). Also partly from French improviser.
Regarded as a foreign word and generally printed in italics in English in early 19c. Other verbs were improvisate (1825), improvisatorize (1828), the latter from improvisator "one of a class of noted extemporaneous poets of Italy" (1765), the earliest word of the group to appear in English. Related: Improvised; improvising.
The metre generally adopted for these compositions was the ottava rima, although Doni affirms that the Florentines used to improvise* in all kinds of measure.
* This new-coined verb is introduced to avoid circumlocution, for this time only: therefore I hope your readers will excuse it. I conjugate it after the regular verb to revise -- improvise -- improvising -- improvised. ["On the Improvvisatori of Italy," in "The Athenaeum," August 1808]
Our travellers have introduced among us the substantive improvisatore unaltered from the Italian; but as the verb improvisare could not be received without alteration, we lack it altogether, though the usage of the noun requires that of the verb: I here endeavor to supply the deficience by the word improvisate. [Samuel Oliver Jr., "A General, Critical Grammar of the Inglish Language," London, 1825]