Thorny plant — pipe (5)
I believe the answer is:
briar
This clue is a double definition.
'thorny plant' is the first definition.
(I've seen this in another clue)
'pipe' is the second definition.
(I know that briar is a type of pipe)
(Other definitions for briar that I've seen before include "Tobacco pipe" , "Prickly wooden stem" , "Prickly scrambling shrub" , "that one may smoke" , "Wild rose bush" .)