Obliged to make tax limited (4,5)
I believe the answer is:
Here is my best explanation:
'obliged' is the definition.
('duty-bound' can be a synonym of 'obliged')
'tax limited' is the subsidiary indication.
'tax' becomes 'duty' (duty is a kind of tax).
'limited' becomes 'bound'.
'to make' is the link.
(Another definition for duty bound that I've seen is "Legally obliged".)