Part of collection put back in small room (4)
I believe the answer is:
cell
'small room' is the definition.
(I've seen this before)
'part of collection put back' is the wordplay.
'part of' indicates a hidden word.
'put back' shows that the letters should be reversed in order.
'llec' is hidden in the letters of 'collection'.
'llec' back-to-front is 'CELL'.
'in' acts as a link.
(Other definitions for cell that I've seen before include "Prison accommodation" , "Animal or plant building unit" , "Place for a prisoner" , "Monk's small room" , "may be wet or dry?" .)