Country singer with simple material (8)
I believe the answer is:
cashmere
'material' is the definition.
(cashmere is a kind of material)
'country singer with simple' is the wordplay.
'country singer' becomes 'Cash' (Johnny Cash).
'with' says to put letters next to each other.
'simple' becomes 'mere' (synonyms).
'cash'+'mere'='CASHMERE'
(Other definitions for cashmere that I've seen before include "Fabric from fine goat's wool" , "Soft fabric made from goats' hair" , "See charm (anag)" , "Expensive wool? Search me" , "Fine soft wool for marchese" .)