impromptu

Prompted by the occasion rather than being planned in advance.

Spoken, performed, done, or composed with little or no preparation; extemporaneous.

With little or no preparation; extemporaneously.

Something, such as a speech, that is made or done extemporaneously.

A short composition, especially for the piano, performed in an offhand or extemporized style.

Prompt; offhand; extempore; extemporized for the occasion: as, an impromptu epigram.

Something said or written, played, etc., at the moment, or without previous study or preparation; an extemporaneous composition or performance.

In music: An extemporized composition; an improvisation.

A composition in irregular form, as if extemporized; a fantasia.

Offhand; without previous study or preparation: as, a verse written impromptu.