Reddish brown — tree (8)
I believe the answer is:
chestnut
This clue is a double definition.
'reddish brown' is the first definition.
(I've seen this before)
'tree' is the second definition.
(chestnut tree is a kind of tree)
(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" .)