Victor joins Olga on the river (5)
I believe the answer is:
volga
'the river' is the definition.
(Volga is an example)
'victor joins olga' is the wordplay.
'victor' becomes 'v' (phonetic alphabet: alpha, bravo, charlie etc.).
'joins' means one lot of letters go next to another.
'v'+'olga'='VOLGA'
'on' acts as a link.
(Other definitions for volga that I've seen before include "flow of water" , "runner abroad" , "Major Russian river" , "Russian river, the longest in Europe" , "Europe's longest river" .)