Largest human organ (4)
I believe the answer is:
skin
'largest human organ' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for skin that I've seen before include "Peel; drum head" , "Protective body covering" , "Outer layer of, eg, apple" , "Outer surface" , "Outer layer of tissue" .)