Fine cotton fabric (6)
I believe the answer is:
muslin
'fine cotton fabric' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for muslin that I've seen before include "Gauze-like cloth" , "Fine soft plain-woven cotton fabric of gauzy appearance" , "Lightweight cotton fabric" , "Cotton for veil or strainer" , "Lightweight cotton cloth" .)