Arguments involving a king's duties (7)
I believe the answer is:
tariffs
'duties' is the definition.
('tariff' can be a synonym of 'duty')
'arguments involving a king's' is the wordplay.
'arguments' becomes 'tiffs' (I've seen this before).
'involving' means one lot of letters goes inside another.
'a king' becomes 'ar' (I've seen this in other clues).
'tiffs' enclosing 'ar' is 'TARIFFS'.
(Other definitions for tariffs that I've seen before include "taxes" , "Lists of charges" , "List of customs duties or charges" .)