Stop advertisement (4)
I believe the answer is:
plug
I believe this is a double definition.
'stop' is the first definition.
(I know that plug is a type of stop)
'advertisement' is the second definition.
(a plug is an advert for something)
(Other definitions for plug that I've seen before include "Promote" , "See 19" , "Stopper - advert" , "Stop - advertising" , "Piece of tobacco; block" .)