Brass percussion instrument (6)
I believe the answer is:
cymbal
'brass percussion instrument' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cymbal that I've seen before include "Crashing instrument" , "Percussion instrument like brass plate" , "Disc of metal struck by a percussionist" , "One of clashing pair" , "Percussionist's disc" .)