Stack of the apples (4)
I believe the answer is:
heap
'stack' is the definition.
(I know that stack can be written as heap)
'of the apples' is the wordplay.
'of' indicates a hidden word.
'HEAP' is hidden in the letters of 'the apples'.
(Other definitions for heap that I've seen before include "Wreck of a car" , "Mound, pile" , "good deal" , "Mound, stack" , "Unreliable old car" .)