His part is arranged for a member of the orchestra (7)
I believe the answer is:
harpist
'his part is arranged for a member of the orchestra' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'his part is arranged' is the wordplay.
'is arranged' indicates anagramming the letters.
'his'+'part'='hispart'
'hispart' with letters rearranged gives 'HARPIST'.
Can you help me to learn more?
(Other definitions for harpist that I've seen before include "musician" , "Stringed instrument player" , "Instrumentalist" .)