More beneficial to cure their disorder (9)
I believe the answer is:
healthier
'more beneficial' is the definition.
Both the answer and definition are comparative adjectives. Perhaps they are linked in a way I don't understand?
'cure their disorder' is the wordplay.
'cure' becomes 'heal' (synonyms).
'disorder' indicates anagramming the letters (a disordered version of the letters).
'their' with letters rearranged gives 'thier'.
'heal'+'thier'='HEALTHIER'
'to' is the link.
Can you help me to learn more?
(Other definitions for healthier that I've seen before include "less prone to disease" , "More in the pink" , "Fitter" .)