Central European river (6)
I believe the answer is:
danube
'central european river' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for danube that I've seen before include "River flowing from Black Forest to Black Sea" , "Viennese river" , "South European river" , "5 down's river" , "River flowing through Belgrade, Budapest and Vienna" .)