Gag, wisecrack (4)
I believe the answer is:
joke
This clue is a double definition.
'gag' is the first definition.
(I know that gag is a more specific form of joke)
'wisecrack' is the second definition.
(I've seen this before)
(Other definitions for joke that I've seen before include "something in cracker" , "Amusing quip" , "Quip, witticism" , "guy" , "Witticism, jest" .)