Three trios (5)
I believe the answer is:
nonet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">three trios</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 nonet that I've seen before include "Instrumental group of nine players" , "small band" , "Ennead" , "Tonne (anag.); music for a group" , "Musical group" .)