Largish singing group (5)
I believe the answer is:
octet
'largish singing group' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for octet that I've seen before include "Work for eight players" , "Group of eight musicians" , "Chamber ensemble, a Mendelssohn favourite" , "Group of eight players" , "Set of eight" .)