This end is a long fibre (5)
I believe the answer is:
sisal
'fibre' is the definition.
(sisal is a kind of fibre)
'this end is a long' is the wordplay.
'end' suggests the final letters.
'long' becomes 'l'.
The final letter of 'this' is 's'.
's'+'is'+'a'+'l'='SISAL'
(Other definitions for sisal that I've seen before include "Rope fibre from leaves of tropical plant" , "Agave rope-fibre" , "Plant yielding rope fibre" , "constituent of rope" , "Rope-fibre made from leaves of tropical plant" .)