Numbered musical work (4)
I believe the answer is:
opus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">numbered musical work</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for opus that I've seen before include "Musical piece" , "(Numbered) musical composition" , "Soup (anag.)" , "Showing creative skill" , "Work (of a composer?)" .)