In cupboard is he stacking plates? (6)
I believe the answer is:
dishes
'plates?' is the definition.
(plate is a kind of dish)
'in cupboard is he stacking' is the wordplay.
'in' indicates a hidden word.
'DISHES' can be found hidden inside 'cupboard is he stacking'.
(Other definitions for dishes that I've seen before include "Tableware" , "Containers for food" , "Vessels for serving food" , "Plates or food courses" , "Food plates or what they many contain" .)