Spite, ill-humour (6)
I believe the answer is:
spleen
This clue is a double definition.
'spite' is the first definition.
(thesaurus)
'ill-humour' is the second definition.
(I've seen this before)
(Other definitions for spleen that I've seen before include "Bodily organ associated with bad temper" , "Quick temper -- spite" , "Organ of the body and short temper" , "Bitterness - body organ" , "Organ causing bad temper?" .)