For a group of singers
I believe the answer is:
choral
'for a group of singers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for choral that I've seen before include "Pertaining to a group of singers" , "19's 9th 16" , "... his ninth ..." , "harmonious society" , "Of a singing group" .)