Complete race for some charity (8)
I believe the answer is:
donation
'some charity' is the definition.
(thesaurus)
'complete race' is the wordplay.
'complete' becomes 'do' (doing is a kind of completing).
'race' becomes 'nation' (both can mean a national or ethnic group).
'do'+'nation'='DONATION'
'for' acts as a link.
(Other definitions for donation that I've seen before include "Do anoint by way of a gift" , "An offering or charitable gift" , "Gift of money as to charity" , "present" , "presentation" .)