Concerto instrument (5)
I believe the answer is:
piano
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">concerto instrument</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 piano that I've seen before include "In music, soflty" , "Softly (mus.)" , "Opposite of forte" , "quiet passage" , "Franz Liszt's instrument" .)