Abandon joint set after breaking (8)
I believe the answer is:
jettison
'abandon' is the definition.
(thesaurus)
'joint set after breaking' is the wordplay.
'after' means one lot of letters go next to another.
'breaking' is an anagram indicator.
'joint'+'set'='jointset'
'jointset' with letters rearranged gives 'JETTISON'.
(Other definitions for jettison that I've seen before include "Get rid of" , "Remove" , "Abandon or throw overboard" , "Eject" , "scrap" .)