Classic boulevard liners
I believe the answer is:
elms
'classic boulevard liners' 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 "Trees (of late, prone to disease)" , "Mel's strange trees" , "Deciduous trees with rough serrated leaves" , "Trees sound like Cockney steering devices" , "may have many leaves" .)