Yo-Yo Ma's instrument
I believe the answer is:
cello
'yo-yo ma's instrument' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cello that I've seen before include "big fiddle?" , "Tortelier's instrument" , "Lloyd Webber's instrument" , "String quartet instrument" , "10 [INSTRUMENT]" .)