Grand instrument (5)
I believe the answer is:
piano
'grand instrument' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for piano that I've seen before include "Soft, softly (music)" , "one of 6 [STEINWAYS]" , "Franz Liszt's instrument" , "p (mus.)" , "Stringed instrument - to be played quietly" .)