Spies on family to obtain material (8)
I believe the answer is:
moleskin
'material' is the definition.
(moleskin is a kind of material)
'spies on family' is the wordplay.
'spies' becomes 'moles' (mole is a kind of spy).
'on' is a charade indicator (letters next to each other).
'family' becomes 'kin' (synonyms).
'moles'+'kin'='MOLESKIN'
'to obtain' acts as a link.
(Other definitions for moleskin that I've seen before include "source of warmth" , "Thick piled cotton cloth" , "Fur resembling velvet" , "Strong cotton fabric with soft nap, used for work clothes" , "Furry cotton fabric" .)