extemporaneous

First recorded in 1650–60, from Late Latin 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. Although extempore is an adjective with the very same meaning as extemporaneous, this word is most often used in its adverbial senses: She spoke extempore, and had the audience's rapt attention. 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.