Clarinet piece (4)
I believe the answer is:
reed
'clarinet piece' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for reed that I've seen before include "Tall water-loving grass" , "Film director" , "Tall grass that grows in swamps" , "Bilk had one" , "Clarinet part; plant" .)