Rostropovich's instrument (5)
I believe the answer is:
'rostropovich'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 "Viola's bigger brother?" , "music produced by this?" , "large-scale fiddle" , "Orchestral instrument played between the legs" , "10 [INSTRUMENT]" .)