Keen relish (5)
I believe the answer is:
gusto
'keen relish' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gusto that I've seen before include "Spirit" , "Zest and enjoyment in doing something" , "Showing zest" , "Hearty enjoyment" , "Vigorous and enthusiastic enjoyment" .)