In favour of self-sacrifice (6)
I believe the answer is:
forego
'sacrifice' is the definition.
(to forego something is to give it up)
'in favour of self' is the wordplay.
'in favour of' becomes 'for' (being for a particular cause).
'self' becomes 'ego' (synonyms).
'for'+'ego'='FOREGO'
(Other definitions for forego that I've seen before include "Go without (desirable thing)" , "Go without or precede" , "Go without, give up" , "Relinquish - do without" , "Precede (in place/time)" .)