Nothing found in small department store (5)
I believe the answer is:
depot
'store' is the definition.
(depot can mean a store or warehouse)
'nothing found in small department' is the wordplay.
'nothing' becomes 'o' (O resembles 0).
'found in' means one lot of letters goes inside another.
'small department' becomes 'dept' (I am not sure about the 'small' bit.).
'o' placed into 'dept' is 'DEPOT'.
Can you help me to learn more?
(Other definitions for depot that I've seen before include "Storehouse or warehouse" , "bus terminus" , "Storage base" , "Terminus for transport vehicles" , "Supply base" .)