strongbox

From strong +‎ box. Compare French coffre-fort.

strongbox (plural strongboxes)

1. A sturdy box with a lock, for storing valuables.
   • 1817 December 31 (indicated as 1818), [Walter Scott], Rob Roy. […], volume (please specify |volume=I to III), Edinburgh: […] James Ballantyne and Co. for Archibald Constable and Co. […]; London: Longman, Hurst, Rees, Orme, and Brown, →OCLC:

     An inroad on the strongbox, or an erasure in the ledger, or a missummation in a fitted account, could hardly have surprised him more disagreeably.

• (sturdy box with a lock): safe, safebox