Piquancy is a little exhilarating at first (4)
I believe the answer is:
bite
'piquancy' is the definition.
(I've seen this in another clue)
'little exhilarating at first' is the wordplay.
'little' becomes 'bit' (a little is a bit).
'at first' says to take the initial letters.
The initial letter of 'exhilarating' is 'e'.
'bit'+'e'='BITE'
'is a' is the link.
(Other definitions for bite that I've seen before include "Light meal" , "Punch" , "Injury from teeth" , "champ" , "Cut with the teeth" .)