Keep secret; skin (4)
I believe the answer is:
hide
This clue is a double definition.
'keep secret' is the first definition.
(I've seen this in another clue)
'skin' is the second definition.
(hide is a kind of skin)
(Other definitions for hide that I've seen before include "Animal's tough skin" , "Conceal with leather" , "mask" , "Bury" , "Place to observe wildlife" .)