Fine material cut, so lustrous (7)
I believe the answer is:
silvery
'lustrous' is the definition.
(both can mean shiny)
'fine material cut so' is the wordplay.
'fine material' becomes 'silk' (I've seen this before).
'cut' means to remove the last letter.
'so' becomes 'very' (I've seen this before).
'silk' with its final letter taken off is 'sil'.
'sil'+'very'='SILVERY'
(Other definitions for silvery that I've seen before include "Epithet for the moon" , "Having a clear ringing tone; like a precious metal" , "Like one precious metal" , "Elementary description of moon" , "Having a white lustrous sheen, like the Spire" .)