Caustic account delivered (5)
I believe the answer is:
acrid
'caustic' is the definition.
(I know that caustic can be written as acrid)
'account delivered' is the wordplay.
'account' becomes 'ac' (abbreviation).
'delivered' becomes 'rid' (as in ridding or delivering someone of something).
'ac'+'rid'='ACRID'
(Other definitions for acrid that I've seen before include "Sharp-smelling like smoke" , "Painfully pungent" , "Nastily pungent" , "Sour, pungent" , "Having a bitter smell or taste" .)