safe-deposit box

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A fireproof metal box, usually in a bank vault, for the safe storage of valuables.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A fireproof metal box, stored in a secure vault, for holding personal valuables

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a fireproof metal strongbox (usually in a bank) for storing valuables