Sharp or biting (5)
I believe the answer is:
acerb
I believe this is a double definition.
'sharp' is the first definition.
(synonyms)
'biting' is the second definition.
(I've seen this in another clue)
(Other definitions for acerb that I've seen before include "sharp" , "Sour, bitter" , "tart" , "harsh and bitter" .)