Rejoicing until jab is thrown (8)
I believe the answer is:
jubilant
'rejoicing' is the definition.
(I know that rejoicing can be written as jubilant)
'until jab is thrown' is the wordplay.
'is thrown' is an anagram indicator (letters thrown around).
'until'+'jab'='untiljab'
'untiljab' is an anagram of 'JUBILANT'.
(Other definitions for jubilant that I've seen before include "In transport" , "Triumphantly joyful" , "Ecstatic" , "Cock-a-hoop" , "Overjoyed" .)