Fibre (5)
I believe the answer is:
sisal
'fibre' is the definition.
(I know that sisal is a type of plant fiber)
This is the entire clue.
(Other definitions for sisal that I've seen before include "Hemp fibre" , "Rope-fibre made from leaves of tropical plant" , "Rope fibre from leaves of tropical plant" , "constituent of rope" , "Agave rope-fibre" .)