Silver copy that is wide open (5)
I believe the answer is:
agape
'wide open' is the definition.
(I've seen this before)
'silver copy' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'copy' becomes 'ape' (ape can mean to copy or imitate).
'ag'+'ape'='AGAPE'
'that is' is the link.
(Other definitions for agape that I've seen before include "love a Christian shows" , "ecclesiastical feast" , "love feast" , "Astonished" , "the love of God!" .)