Keen enjoyment (4)
I believe the answer is:
zest
'keen enjoyment' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for zest that I've seen before include "Orange or lemon peel" , "Relish, enthusiasm" , "Grated lemon skin" , "Drive" , "Great energy; citrus peel" .)