Of a group of singers (6)
I believe the answer is:
choral
'of a group of singers' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for choral that I've seen before include "Engaged in singing" , "19's 9th 16" , "Written to be performed by a choir" , "Sung by group of singers" , "Sung psalm" .)