Citizen having say in veto (8)
I believe the answer is:
negative
'veto' is the definition.
(I know that veto can be written as negative)
'citizen having say' is the wordplay.
'citizen' becomes 'native' (I can't explain this - if you can you should give a lot more credence to this answer).
'having' is an insertion indicator.
'say' becomes 'eg' (both can mean 'for example').
'native' enclosing 'eg' is 'NEGATIVE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for negative that I've seen before include "image for a developer" , "Denying" , "Early form of photo" , "Opposite of affirmative" , "Piece of photographic film" .)