Instrument in small room close to piano (5)
I believe the answer is:
Here is my best explanation:
'instrument' is the definition.
(cello is a kind of instrument)
'small room close to piano' is the subsidiary indication.
'small room' becomes 'cell' (I've seen this before).
'close to' suggests the final letters (the \'close\' to the word).
The final letter of 'piano' is 'o'.
'in' is the link.
(Other definitions for cello that I've seen before include "Lloyd Webber's instrument", "has strings attached", "Tortelier's instrument", "Bowed musical instrument", "10 [INSTRUMENT]", "It's bigger than a viola, but smaller than a double bass", "music produced by this?", "Large stringed instrument", "Instrument like large violin held between the knees" and "Viola's bigger brother?".)