Singer has trios performed for another (9)
I believe the answer is:
chorister
'for another' is the definition.
I can't tell whether this definition defines the answer.
'singer has trios performed' is the wordplay.
'singer' becomes 'cher' (Cher is a US musician).
'has' is an insertion indicator.
'performed' is an anagram indicator.
'trios' is an anagram of 'orist'.
'cher' going around 'orist' is 'CHORISTER'.
Can you help me to learn more?
(Other definitions for chorister that I've seen before include "Church, cathedral singer" , "Boy in church" , "Boy singing" , "Choir member" , "Choirboy or girl" .)