Colonnade tree (3)
I believe the answer is:
elm
'colonnade tree' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for elm that I've seen before include "Kind of tree" , "Deciduous tree with light serrated leaves" , "Gray's rugged tree (Elegy)" , "Furniture wood" , "Tall shade tree" .)