Rehearsals in part for organs (4)
I believe the answer is:
ears
'organs' is the definition.
(ear is a kind of organ)
'rehearsals in part' is the wordplay.
'in part' says the answer is hidden in the clue.
'EARS' is hidden within 'rehearsals'.
'for' acts as a link.
(Other definitions for ears that I've seen before include "''He who has ... to hear, let him hear'' (bible)" , "Shakespeare 'Friends, Romans, countrymen, lend me your . . . .'" , "Auditors" , "Organs for 7 down" , "Lugholes" .)