Pastoral pipe (4)
I believe the answer is:
reed
'pastoral pipe' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reed that I've seen before include "It grows in water or marshy land" , "Blade of tall marsh grass" , "Vibrator in the mouthpiece of a wind instrument" , "Clarinet part; plant" , "Film director" .)