National tax (4)
I believe the answer is:
scot
I believe this clue is a double definition.
'national' is the first definition.
(I've seen this in other clues)
'tax' is the second definition.
(thesaurus)
(Other definitions for scot that I've seen before include "Northerner; old tax" , "---- free: originally free from penalties of taxation" , "Payment" , "Aberdonian possibly" , "Rabbie Burns, for instance" .)