Choir plan working with him and orchestra? (12)
I believe the answer is:
philharmonic
'orchestra?' is the definition.
(I know that philharmonic is a type of orchestra)
'choir plan working with him' is the wordplay.
'working with' is an anagram indicator (working with the letters).
'choir'+'plan'='choirplan'
'choirplan' anagrammed with 'him' makes 'PHILHARMONIC'.
'and' acts as a link.
(Other definitions for philharmonic that I've seen before include "Devoted to music (used in orchestra names)" , "Word found in the title of many orchestras (literally, devoted to music)" , "Music-loving" .)