Promote - stopper (4)
I believe the answer is:
plug
I believe this is a double definition.
'promote' is the first definition.
(plugging is a kind of promoting)
'stopper' is the second definition.
(synonyms)
(Other definitions for plug that I've seen before include "Fitment at the end of a flex" , "Promote" , "Favourable mention" , "Stopper - publicise" , "Mention favourably - stopper" .)