Pound for a plug? (4)
I believe the answer is:
quid
I believe this is a double definition.
'pound' is the first definition.
('quid' can be a synonym of 'pound')
'a plug?' is the second definition.
('quid' can be a synonym of 'plug')
'for' is the link.
(Other definitions for quid that I've seen before include "plug?" , "PS (sl.)" , "1 GBP - piece of chewing tobacco" , "bit of bread" , "Bit of greens" .)