Different matter, hospital department providing therapy (9)
I believe the answer is:
treatment
'therapy' is the definition.
(I know that therapy can be written as treatment)
'different matter hospital department' is the wordplay.
'different' indicates an anagram (letters placed in a different order).
'hospital department' becomes 'ENT' (Ear, Nose and Throat).
'matter' is an anagram of 'treatm'.
'treatm'+'ent'='TREATMENT'
'providing' acts as a link.
(Other definitions for treatment that I've seen before include "Medical care for injury" , "Care provided to improve a situation" , "Application of remedy" , "The handling or management of something" , "prescribed drugs possibly" .)