Hammered instrument (8)
I believe the answer is:
dulcimer
'hammered instrument' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for dulcimer that I've seen before include "Mild cure for musical instrument" , "Stringed instrument played with hammers" , "Hammered instrument" , "Old percussion instrument" , "Instrument of Xanadu damsel (Coleridge)" .)