Weep on platinum vault (5)
I believe the answer is:
crypt
'vault' is the definition.
(I've seen this before)
'weep on platinum' is the wordplay.
'weep' becomes 'cry' (synonyms).
'on' is a charade indicator (letters next to each other).
'platinum' becomes 'pt' (chemical symbol).
'cry'+'pt'='CRYPT'
(Other definitions for crypt that I've seen before include "Burial vault" , "Underground church vault" , "Tomb" , "Underground chapel" , "Undeground room" .)