Instrument played while seated (5)
I believe the answer is:
cello
'instrument played while seated' 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 "Tortelier's instrument" , "It's bigger than a viola, but smaller than a double bass" , "Viola's bigger brother?" , "10 [INSTRUMENT]" , "Bass stringed instrument" .)