On the subject of surplus (4)
I believe the answer is:
over
This could be a double definition.
'on' is the first definition.
(I've seen this in other clues)
'subject of surplus' is the second definition.
'over' can be an answer for 'surplus' (I've seen this in another clue). I am not certain of the 'subject of' bit.
'the' is the link.
Can you help me to learn more?
(Other definitions for over that I've seen before include "Having gone < to America" , "Finished-up -left" , "Action far more drastic than necessary" , "Accomplished" , "Given too much money" .)