River of York (4)
I believe the answer is:
ouse
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">river of york</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 ouse that I've seen before include "York's river" , "bird has lost its tail" , "River of 1 across" , "English river, sounds as if it flows slowly" , "River at Lewes (Sussex)" .)