Small pie (4)
I believe the answer is:
tart
'small pie' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tart that I've seen before include "loose woman" , "A bit sour, like flattish pie" , "Acid-tasting; pastry" , "Sour-tasting pie?" , "Acidic; pastry dish" .)