1. the chamber in a furnace, stove, or steam engine where fuel is burned
2. a fireproof container or safe for storing important documents

Examples

• The coal was shoveled into the locomotive’s firebox.
• He opened the firebox to add more wood to the fire.
• The steam engine’s firebox glowed red hot.
• She kept her birth certificate in a small firebox.
• The old furnace had a large cast-iron firebox.
• Important papers should be stored in a firebox for protection.
• The firebox door was heavy and required both hands to open.