Copying fastener in silver (5)
I believe the answer is:
aping
'copying' is the definition.
('ape' can be a synonym of 'copy')
'fastener in silver' is the wordplay.
'fastener' becomes 'pin' (pin is a kind of fastener).
'in' means one lot of letters goes inside another.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'pin' going into 'ag' is 'APING'.
(Other definitions for aping that I've seen before include "Acting like a parrot" , "Imitation" , "Sending up" , "Taking off" , "Trying to repeat" .)