Suppress a joke (3)
I believe the answer is:
gag
This clue is a double definition.
'suppress' is the first definition.
(thesaurus)
'a joke' is the second definition.
('gag' can be a synonym of 'joke')
(Other definitions for gag that I've seen before include "Muffle with slang joke" , "Make quiet" , "Prevent from speaking freely" , "Shut up" , "Joke; smother" .)