Way to halve material used up in store (6)
I believe the answer is:
larder
'store' is the definition.
(food store)
'way to halve material used up in' is the wordplay.
'way' becomes 'rd' (short for road).
'to halve material' becomes 'real' (I can't justify this - if you can you should give a lot more credence to this answer).
'used up' says the letters should be written backwards (in a down clue, letters go up).
'in' is an insertion indicator.
'real' backwards is 'laer'.
'rd' going within 'laer' is 'LARDER'.
Can you help me to learn more?
(Other definitions for larder that I've seen before include "Room or cupboard for food storage" , "Cool store" , "Stock of provisions" , "Small room for storing food" , "Place where food is kept" .)