Opposite where one is served (7)
I believe the answer is:
counter
'opposite' is the definition.
(I've seen this before)
'one is served' is the wordplay.
I cannot really see how this works, but
'one' could be 'un' (northern English dialect form of 'one') and 'un' is found in the answer.
This explanation may well be incorrect...
'where' acts as a link.
Can you help me to learn more?
(Other definitions for counter that I've seen before include "Tiddlywink" , "Oppose; bar; disc" , "check" , "Sales desk" , "Obverse" .)