Ordinary German word for the river (4)
I believe the answer is:
oder
'river' is the definition.
(River Oder in central Europe)
'ordinary german word for' is the wordplay.
'ordinary' becomes 'O' (abbreviation e.g. O-Levels).
'german word for' becomes 'der' (I can't justify this - if you can you should believe this answer much more).
'o'+'der'='ODER'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for oder that I've seen before include "River flowing into the Baltic" , "German and Polish river" , "European flower" , "River forming northern part of the German-Polish border" , "River on border of Poland and Germany" .)