Singer his rector trained (9)
I believe the answer is:
chorister
'singer' is the definition.
(chorister is a kind of singer)
'his rector trained' is the wordplay.
'trained' indicates an anagram (to train can mean to grow something into a shape).
'his'+'rector'='hisrector'
'hisrector' is an anagram of 'CHORISTER'.
(Other definitions for chorister that I've seen before include "Boy singing" , "Church, cathedral singer" , "Choir member" , "Choirboy or girl" , "Boy singer" .)