Central layer in downy outer skin (4)
I believe the answer is:
rind
'skin' is the definition.
(synonyms)
'central layer in downy outer' is the wordplay.
'outer' indicates the answer is hidden within the clue (I've seen 'out of' mean this).
'RIND' is hidden in the letters of 'central layer in downy'.
(Other definitions for rind that I've seen before include "tough skin" , "Skin of orange or melon" , "Hard outer skin, of an orange say" , "Outer skin of citrus fruit" , "Protective cover on cheese" .)