Brilliant success (5)
I believe the answer is:
eclat
'brilliant success' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eclat that I've seen before include "Brilliant display -- conspicuous success" , "Brilliance" , "Splendour; renown" , "Enthusiastic approval" , "Showy effect (Fr.)" .)