Citrus cover (4)
I believe the answer is:
rind
'citrus cover' 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 "'Peel, bark (4)'" , "Outer layer (of cheese)" , "tough skin" , "Cheese or fruit skin" , "The peel of a fruit" .)