Stop a promotion (4)
I believe the answer is:
plug
I believe this is a double definition.
'stop' is the first definition.
(plug is a kind of stop)
'a promotion' is the second definition.
(plug is a kind of promotion)
(Other definitions for plug that I've seen before include "Blatant promotion" , "Mention favourably - stopper" , "Bung -- promotion" , "Power point" , "Piece of chewing tobacco" .)