Shed, with "off" (6)
I believe the answer is:
'shed with off' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slough that I've seen before include "Swamp; shed (dead skin)" , "shed covering" , "Swamp; Berkshire town" , "Berkshire town - bog - shed" , "poet wanted destroyed" .)