Synthetic fibre; paint (7)
I believe the answer is:
acrylic
I believe this is a double definition.
'synthetic fibre' is the first definition.
(I've seen this before)
'paint' is the second definition.
(acrylic paint is a kind of paint)
(Other definitions for acrylic that I've seen before include "fibre that's synthetic" , "Synthetic fibre or paint" , "The synthetic fibre is icy, Carl" , "Synthetic resin or fibre used for textiles" , "Kind of paint" .)