Free on account: bitter (5)
I believe the answer is:
acrid
'bitter' is the definition.
(I know that bitter can be written as acrid)
'free on account' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'on' says to put letters next to each other.
'account' becomes 'ac' (abbreviation).
'rid' after 'ac' is 'ACRID'.
(Other definitions for acrid that I've seen before include "Having a bitter smell or taste" , "Bitter in smell, like smoke" , "Bitter - pungent" , "Unpleasantly pungent" , "irritating" .)