Buck turned on organ pipe (4)
I believe the answer is:
reed
'organ pipe' is the definition.
(thesaurus)
'buck turned' is the wordplay.
'buck' becomes 'deer' (buck can mean a male deer).
'turned' says the letters should be written backwards.
'deer' backwards is 'REED'.
'on' is the link.
(Other definitions for reed that I've seen before include "Marsh plant with straight hollow stem" , "Coarse grass in the organ pipe" , "Slender grass of wet areas" , "Tall water-loving grass" , "Tall grass plant that grows in water" .)