Bit of wordplay (3)
I believe the answer is:
'bit of wordplay' is the definition.
(punning is a type of wordplay)
This is all the clue.
(Other definitions for pun that I've seen before include "Double entendre" , "A play on words, may be funny" , "Humorous play on words" , "Bit of paronomasia; witticism" , "Humorous wordplay" .)