Casual fabric (5)
I believe the answer is:
denim
'casual fabric' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for denim that I've seen before include "Material for casual trousers or jackets" , "Hard-wearing cloth" , "Tough cotton fabric" , "Hard-wearing clothing material, twilled cotton" , "Coloured cotton twill" .)