Edge has broken some pieces of glass instrument (8)
I believe the answer is:
panpipes
'instrument' is the definition.
(I've seen this before)
'edge has broken some pieces of glass' is the wordplay.
'edge' becomes 'pip' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'has broken' indicates putting letters inside (inserted letters break in).
'some pieces of glass' becomes 'panes' (I've seen this in another clue).
'pip' inserted within 'panes' is 'PANPIPES'.
Can you help me to learn more?
(Other definitions for panpipes that I've seen before include "Musical instrument made of reeds of different lengths" , "Musical wind instrument - syrinx" , "Simple wind instrument" , "Folk instrument" , "Primitive wind instrument" .)