Violin string material (6)
I believe the answer is:
catgut
'violin string material' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for catgut that I've seen before include "Material used for violin strings, for example" , "stringy material" , "Tough string for stitches and musical instruments" , "Cord used for stringing instruments and rackets" , "Natural material for violin strings" .)