Brilliant display or effect (5)
I believe the answer is:
eclat
I believe this clue is a double definition.
'brilliant display' is the first definition.
(I've seen this before)
'effect' is the second definition.
(I have seen 'Brilliant effect' mean 'eclat' so perhaps 'effect' could also mean 'eclat')
(Other definitions for eclat that I've seen before include "Social distinction in France" , "Splash" , "great success" , "Distinguished success" , "Acclaim; showy display" .)