spur-of-the-moment, spontaneously, ad lib, ad libitum, unprepared, improvisate, improviso, ex tempore, improvisatorial, imprompt, more...

planned, premeditated, prepared, extemporaneous

speech, performance, skit, debate, presentation, stand-up comedy, storytelling, poetry reading, more...

little, flat, first, second, brilliant, sharp, major, fantaisie, fantasie, fantasy, clever

spontaneous reply,   acting on the spot,   quickly gathered,   without forethought,   quickly thought,   without rehearsal,   on a fly,   an unpanned meeting,   spontaneous version