A victory on river (4)
I believe the answer is:
avon
'river' is the definition.
(I know that Avon is a river)
'a victory on' is the wordplay.
'victory' becomes 'v'.
'a'+'v'+'on'='AVON'
(Other definitions for avon that I've seen before include "English river, flows through Stratford" , "River running through Bath" , "River of the Bard" , "Shakespeare its swan" , "Stratford's river" .)