Crease on the back of spun fabric (5)
I believe the answer is:
linen
'fabric' is the definition.
(I know that linen is a type of fabric)
'crease on the back of spun' is the wordplay.
'crease' becomes 'line' (synonyms).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'the back of' indicates one should take the final letters.
The final letter of 'spun' is 'n'.
'line'+'n'='LINEN'
(Other definitions for linen that I've seen before include "Sheets, tablecloth etc." , "clothes and sheets" , "Sheets, pillowcases etc" , "underwear" , "Flaxen fabric" .)