Sheer fabric of silk or rayon (7)
I believe the answer is:
'sheer fabric of silk or rayon' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for chiffon that I've seen before include "Fine transparent fabric" , "Fine material" , "Light silk/nylon fabric" , "Sheer silk or rayon fabric" , "Fine (semi)transparent fabric" .)