Piece for eight (5)
I believe the answer is:
octet
'piece for eight' 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 "A group of eight, may be singers" , "Chamber ensemble, a Mendelssohn favourite" , "Musical composition for eight performers" , "Lines of verse" , "Set of eight" .)