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