extemporaneous

First recorded in 1650–60, extemporaneous is from the Late Latin word extemporāneus on the spur of the moment. See extempore, -an, -eous

1, 2. Extemporaneous ( extempore ), impromptu, improvised are used of expression given without preparation or only partial preparation. Extemporaneous and impromptu may both refer to speeches given without any preparation: an extemporaneous ( impromptu ) speech. Extemporaneous may also refer to a speech given from notes or an outline: extemporaneous lectures. Impromptu also refers to poems, songs, etc., delivered without preparation and at a moment's notice. Improvised is applied to something composed (recited, sung, acted), at least in part, as one goes along: an improvised piano accompaniment.

1. memorized.