Plug or bung (7)
I believe the answer is:
stopper
This clue is a double definition.
'plug' is the first definition.
(I know that stopper is a type of plug)
'bung' is the second definition.
(I know that Stopper is a bung)
(Other definitions for stopper that I've seen before include "Perhaps cork" , "Plug for a bottle" , "One blocks" , "Maybe cork" , "Cork - goalkeeper?" .)