Row over origin of nylon fabric (5)
I believe the answer is:
linen
'fabric' is the definition.
(linen is a kind of fabric)
'row over origin of nylon' is the wordplay.
'row' becomes 'line' (as in a row of things).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'origin of' says to take the initial letters.
The initial letter of 'nylon' is 'n'.
'line'+'n'='LINEN'
(Other definitions for linen that I've seen before include "Lenin (anag) -- fabric" , "Sheets, tablecloth etc." , "Bed sheets etc" , "Sheets, cloths, napkins etc" , "Flax product" .)