Metallica finally exiting festival compound (5)
I believe the answer is:
ester
'compound' is the definition.
(ester is a kind of compound)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for ester that I've seen before include "Chemical compound of acid and alcohol, found in trees" , "Organic compound, rhymes with court joker" , "radical" , "Reset (anag.)" , "Fat" .)