Advertise bung (4)
I believe the answer is:
plug
I believe this clue is a double definition.
'advertise' is the first definition.
(plugging is a kind of advertizing)
'bung' is the second definition.
(I've seen this before)
(Other definitions for plug that I've seen before include "Stuff" , "Stopper - connector" , "Favourable mention" , "Shoot" , "Device put into socket" .)