Abuse one's urge to be magnanimous (8)
I believe the answer is:
generous
'be magnanimous' is the definition.
('generous' can be similar in meaning to 'magnanimous')
'abuse one's urge' is the wordplay.
'abuse' indicates an anagram.
'ones'+'urge'='onesurge'
'onesurge' with letters rearranged gives 'GENEROUS'.
'to' acts as a link.
(Other definitions for generous that I've seen before include "More than adequate" , "Willing to give unstintingly" , "Liberal, bountiful" , "Ample" , "Willing to give unselfishly" .)