Norma, for one (5)
I believe the answer is:
opera
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">norma for one</span>' is the definition.<br/ ><span class="explanation-format__explanation">(Norma is an opera by Vincenzo Bellini)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for opera that I've seen before include "Carmen, perhaps" , "Macbeth for one" , "Eg, Il trovatore" , "Aida, for example" , "eg Otello" .)