River of Central Europe (4)
I believe the answer is:
oder
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">river of central europe</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for oder that I've seen before include "East European river" , "River forming northern part of the German-Polish border" , "School blazer insignia" , "River flowing into the Baltic" , "German river that empties into the Baltic Sea" .)