Burlap fiber (4)
I believe the answer is:
jute
'burlap fiber' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for jute that I've seen before include "Fibre used for making sacking and ropes" , "Old invader of England" , "Fibre-producing plant" , "Plant fibre used in making rope and sacks" , "Companion for Anglo-Saxon" .)