Mall unit (4)
I believe the answer is:
shop
'mall unit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for shop that I've seen before include "Betray - place selling things" , "Store or boutique" , "Establishment for the sale of goods" , "Where goods are bought and sold" , "Inform on; store" .)