Plant fibre (5)
I believe the answer is:
sisal
'plant fibre' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sisal that I've seen before include "Rope fibre from leaves of tropical plant" , "Hemp fibre" , "Natural fibre" , "Agave cultivated for its fibre" , "Agave yielding fibre" .)