Bitter councillor blocking financial support (5)
I believe the answer is:
acrid
'bitter' is the definition.
(I know that bitter can be written as acrid)
'councillor blocking financial support' is the wordplay.
'councillor' becomes 'cr' (abbreviation).
'blocking' means one lot of letters goes inside another (to block can mean to plug a gap in something).
'financial support' becomes 'aid' (I've seen this in another clue).
'cr' inserted into 'aid' is 'ACRID'.
(Other definitions for acrid that I've seen before include "Pungent or sharp, like smoke" , "Stinging" , "Having a bitter taste or small, like smoke" , "Sarcastic" , "Bitter or corrosive" .)