Organ next to the stomach (6)
I believe the answer is:
spleen
'organ next to the stomach' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spleen that I've seen before include "Quick temper -- spite" , "Quick temper - body organ" , "Ill-temper" , "Internal organ - irascibility" , "Soft organ near the stomach" .)