Improve his disposition with an opposite result (10)
I believe the answer is:
impoverish
'an opposite result' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how one could define the other.
'improve his disposition' is the wordplay.
'disposition' is an anagram indicator.
'improve'+'his'='improvehis'
'improvehis' with letters rearranged gives 'IMPOVERISH'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for impoverish that I've seen before include "beggar" , "Spoil the quality of" , "Make poor" .)