Bitter account to deliver! (5)
I believe the answer is:
acrid
'bitter' is the definition.
(thesaurus)
'account to deliver' is the wordplay.
'account' becomes 'ac'.
'to deliver' becomes 'rid' (as in 'deliver us from evil').
'ac'+'rid'='ACRID'
(Other definitions for acrid that I've seen before include "Having a bitter taste or small, like smoke" , "Having a bitter smell or taste" , "Bitter - caustic" , "Sharp - biting" , "Greek goddess" .)