Instrument that might be grand (5)
I believe the answer is:
piano
I believe this clue is a double definition.
'instrument' is the first definition.
(I know that piano is a type of stringed instrument)
'grand' is the second definition.
(thesaurus)
'that might be' acts as a link.
(Other definitions for piano that I've seen before include "quiet passage" , "Upright type?" , "Direction in music (1): relatively softly" , "Softly, musically speaking" , "one of 6 [STEINWAYS]" .)