Wood used by barrel maker (3)
I believe the answer is:
elm
'wood' is the definition.
(elm is a kind of wood)
'used by barrel maker' is the wordplay.
'used by' says the answer is hidden in the clue.
'ELM' is hidden within 'barrel maker'.
(Other definitions for elm that I've seen before include "Kind of tree" , "Source of timber" , "Leaving body" , "Gray's rugged tree (Elegy)" , "Deciduous tree with light serrated leaves" .)