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