Make bitter expert send brat east (8)
I believe the answer is:
acerbate
'make bitter' is the definition.
(synonyms)
'expert send brat east' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'send' is an anagram indicator (I've seen 'sends' mean this (send can mean excite or stir)).
'east' becomes 'e' (abbreviation).
'brat' is an anagram of 'rbat'.
'ace'+'rbat'+'e'='ACERBATE'
(Other definitions for acerbate that I've seen before include "Put out" , "distress" , "Exasperate" .)