Musical piece for two (4)
I believe the answer is:
duet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">musical piece for two</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for duet that I've seen before include "Composition for two performers" , "Work for two players" , "Work for two performers" , "Musical piece for two performers" , "Piece for brace" .)