Reddish brown — tree (8)
I believe the answer is:
chestnut
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">reddish brown</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">tree</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(chestnut tree is a kind of tree)</span><br/ ><br/ ></span>
(Other definitions for chestnut that I've seen before include "''Underneath the spreading . . . . . . . . tree''" , "comedian's overused line?" , "Sweet -; horse -; water -" , "Old story" , "Deep reddish-brown" .)