Sail-cloth (6)
I believe the answer is:
canvas
I believe this clue is a double definition.
'sail' is the first definition.
(I know that sail can be written as canvas)
'cloth' is the second definition.
(I know that canvas is a type of piece of cloth)
(Other definitions for canvas that I've seen before include "End of a racing boat; coarse cloth" , "Sail material" , "Cloth for painting etc" , "Given a hearing, thoroughly discuss" , "Floor of a boxing ring" .)