Zip into department store (5)
I believe the answer is:
depot
'store' is the definition.
(depot can mean a store or warehouse)
'zip into department' is the wordplay.
'zip' becomes 'o' (zip can mean zero).
'into' means one lot of letters goes inside another.
'department' becomes 'dept'.
'o' inserted within 'dept' is 'DEPOT'.
(Other definitions for depot that I've seen before include "Depository for goods" , "Regimental HQ" , "Storage location" , "Storehouse or main bus station (5)" , "Storehouse, repository" .)