Bitterly pungent (5)
I believe the answer is:
acrid
'bitterly pungent' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for acrid that I've seen before include "Direly pungent" , "Astringent" , "Strong and sharp" , "irritating" , "Bitterly pungent" .)