Joke; silence (3)
I believe the answer is:
gag
I believe this is a double definition.
'joke' is the first definition.
(a gag is a joke or witticism)
'silence' is the second definition.
(gagging is a kind of silencing)
(Other definitions for gag that I've seen before include "Joke (colloq.)" , "Censor" , "that renders one speechless" , "Joke; silencer" , "Joke or muffler - a palindrome" .)