Bill gets free bitter (5)
I believe the answer is:
acrid
'bitter' is the definition.
(I know that bitter can be written as acrid)
'bill gets free' is the wordplay.
'bill' becomes 'ac' (short for account).
'gets' says to put letters next to each other.
'free' becomes 'rid' (to be free of something is to be rid of it).
'ac'+'rid'='ACRID'
(Other definitions for acrid that I've seen before include "Strong and sharp-smelling" , "Bitter - pungent" , "irritating" , "Unpleasantly bitter" , "Pungent; caustic" .)