Watermelon covering (4)
I believe the answer is:
rind
'watermelon covering' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rind that I've seen before include "outside" , "Outer layer (of cheese)" , "The peel of a fruit" , "Crust" , "Fruit skijn as of orange" .)