Instrument some collected, sent back (5)
I believe the answer is:
cello
'instrument' is the definition.
(cello is a kind of instrument)
'some collected sent back' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'sent back' shows that the letters should be reversed in order.
'ollec' can be found hidden inside 'collected'.
'ollec' in reverse letter order is 'CELLO'.
(Other definitions for cello that I've seen before include "Jacqueline du Pre's instrument" , "String quartet instrument" , "Music-maker" , "has strings attached" , "Tortelier's instrument" .)