Hide under excessive clothing (8)
I believe the answer is:
overcoat
'clothing' is the definition.
(type of clothing)
'hide under excessive' is the wordplay.
'hide' becomes 'coat' (an animal's coat).
'under' means one lot of letters go next to another.
'excessive' becomes 'over' (over can mean in excess or excessively).
'coat' put after 'over' is 'OVERCOAT'.
(Other definitions for overcoat that I've seen before include "Ulster, perhaps" , "Clobber" , "Evocator (anag.)" , "Warm garment" , "Ulster, for example" .)