Piquancy; citrus peel (4)
I believe the answer is:
zest
I believe this is a double definition.
'piquancy' is the first definition.
(I know that piquancy can be written as zest)
'citrus peel' is the second definition.
(I've seen this in another clue)
(Other definitions for zest that I've seen before include "Grated lemon skin" , "Orange-peel" , "Zing" , "Vigour" , "Spirit" .)