Scotland’s longest river (3)
I believe the answer is:
tay
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">scotland's longest river</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 tay that I've seen before include "Bridge at Dundee" , "Longest Scottish river" , "Dundee's river" , "Scotland's longest river" , "Scottish river and firth" .)