Extempore
I believe the answer is:
impromptu
'extempore' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for impromptu that I've seen before include "Without pre-planning" , "Unscripted" , "Off-the-cuff" , "unrehearsed piece" , "Spontaneously, off the cuff" .)