Lawn tree (3)
I believe the answer is:
'lawn 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 "Tree of the genus Ulmus" , "Perennial plant" , "Tree with winged fruit" , "Deciduous tree with rough serrated leaves" , "Victim of fungus" .)