Composer's work (4)
I believe the answer is:
opus
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">composer's work</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for opus that I've seen before include "Musical piece" , "Work (mus.)" , "(Numbered) musical composition" , "Piece of music (with number)" , "Composer's work" .)