Brier feature (5)
I believe the answer is:
thorn
'brier feature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for thorn that I've seen before include "Invariable accompaniment of 2, they say" , "Sharp woody projection" , "Letter written long ago" , "Cause of grief" , "North (anag) -- point" .)