Tulip tree (6)
I believe the answer is:
poplar
'tulip tree' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for poplar that I've seen before include "Tree, maybe from Lombardy" , "The tree that quivers" , "Tall, slender tree" , "Tree of willow family" , "part of our capital" .)