Profitable hostilities with Dutch essential to troubled reign (9)
I believe the answer is:
rewarding
'profitable' is the definition.
(similar in meaning)
'hostilities with dutch essential to troubled reign' is the wordplay.
'hostilities' becomes 'war' (hostilities between two nations).
'with' says to put letters next to each other.
'dutch' becomes 'd' (common abbreviation).
'essential to' means one lot of letters goes inside another (inserted letters contained by essential to others).
'troubled' is an anagram indicator.
'war'+'d'='ward'
'reign' anagrammed gives 'reing'.
'ward' inserted inside 'reing' is 'REWARDING'.
(Other definitions for rewarding that I've seen before include "Providing personal satisfaction" , "worthwhile" , "Well worth doing for its own sake" , "Satisfying, well worth doing" , "profitable" .)