The rancour that comes from an unfavourable disposition of one's effects (7)
I believe the answer is:
illwill
'the rancour that comes from an unfavourable' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'disposition of one's effects' is the wordplay.
I cannot really see how this works, but
'disposition' could be 'will' (I have seen 'Final disposition' mean 'will' so perhaps 'disposition' could also mean 'will') and 'will' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for illwill that I've seen before include "bad blood" , "Hatred" .)