Slough outbuilding (4)
I believe the answer is:
shed
I believe this clue is a double definition.
'slough' is the first definition.
('shed' can be a synonym of 'slough')
'outbuilding' is the second definition.
(shed is a kind of outbuilding)
(Other definitions for shed that I've seen before include "made redundant" , "Discarded" , "place for bikes" , "Cast - shine" , "Outhouse for storing garden tools etc" .)