Great river (6)
I believe the answer is:
amazon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">great river</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 amazon that I've seen before include "very long river" , "Female warrior of Greek myth" , "seller on the Internet" , "Net giant" , "banker" .)