Chamber piece (4)
I believe the answer is:
trio
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">chamber piece</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 trio that I've seen before include "Archduke, possibly" , "Three together" , "Beethoven's 'Archduke', for instance" , "Musical group" , "Chamber group" .)