Mist over large tree (5)
I believe the answer is:
hazel
'tree' is the definition.
(hazel tree is a kind of tree)
'mist over large' is the wordplay.
'mist' becomes 'haze' (I've seen this before).
'over' means one lot of letters go next to another.
'large' becomes 'l'.
'haze'+'l'='HAZEL'
(Other definitions for hazel that I've seen before include "Filbert" , "Tree - greenish-brown" , "Catkin-bearing tree" , "Tree; girl's name" , "Nut tree" .)