Biting pie (4)
I believe the answer is:
tart
This clue is a double definition.
'biting' is the first definition.
(I've seen this before)
'pie' is the second definition.
(I know that tart is a type of pie)
(Other definitions for tart that I've seen before include "Acid-tasting; pastry" , "Pie with fruit filling" , "A bit sour like open cake" , "Bitter - pudding" , "See 10" .)