Abdominal organ — bad temper (6)
I believe the answer is:
spleen
I believe this clue is a double definition.
'abdominal organ' is the first definition.
(I've seen this in another clue)
'bad temper' is the second definition.
(informal term for bad temper)
(Other definitions for spleen that I've seen before include "Internal organ - irascibility" , "Organ of the body - ill temper" , "Body organ; spite" , "Organ causing bad temper?" , "Acrimony" .)