Flay – fruit peel (4)
I believe the answer is:
This clue is a double definition.
'flay' is the first definition.
(I know that flay is a kind of skin)
'fruit peel' is the second definition.
(I've seen this in another clue)
(Other definitions for skin that I've seen before include "Thin outer layer" , "Outer layer of, eg, apple" , "External surface" , "Fell" , "External membrane of body" .)