Jokester (3)
I believe the answer is:
wag
'jokester' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for wag that I've seen before include "He must be joking" , "Vibrate; jester" , "Shake" , "Oscillate - wit" , "Wave to and fro, as a dog's tail" .)