Spontaneous remark (2-3)
I believe the answer is:
ad lib
'spontaneous remark' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ad lib that I've seen before include "Off the cuff remark" , "Spontaneously" , "Speak off the cuff, unrehearsed" , "As much as you want" , "One's not prepared to do it" .)