German-Polish border river (4)
I believe the answer is:
oder
'german-polish border river' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oder that I've seen before include "Rode around the European river" , "German banker" , "River forming northern part of the German-Polish border" , "East European river" , "Polish/German river" .)