River of Aragon (4)
I believe the answer is:
ebro
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">river of aragon</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ebro that I've seen before include "Longest river in Spain" , "European runner" , "Border Hannibal crossed" , "Spanish river" , "flower" .)