Group of eight performers (5)
I believe the answer is:
octet
'group of eight performers' 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 "Mendelssohn or Schubert piece" , "What takes members up to eighth" , "Group of eight musicians" , "Mendelssohn wrote this" , "Played" .)