Yule greenery (5)
I believe the answer is:
holly
'yule greenery' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for holly that I've seen before include "Prickly-leaved shrub" , "Prickly plant" , "Shrub with red berries" , "Evergreen tree associated with Christmas" , "Prickly evergreen" .)