Big shade trees (4)
I believe the answer is:
elms
'big shade trees' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for elms that I've seen before include "Deciduous trees with rough serrated leaves" , "Mel's strange trees" , "Trees (of late, prone to disease)" , "may have many leaves" , "rugged feature of country churchyard" .)