A strongbox is a small, heavy box — almost always metal — that you lock things inside. The point is that the box itself is hard to break open, so what is inside stays safe: money, gold, jewellery, land papers, a will. It is a box you can carry, or at least two people can carry, which is exactly how it differs from a safe built into a wall. The word feels old. In real life today, people say 'safe' for the thing in a hotel room or a bedroom cupboard, and 'strongbox' shows up mostly in stories — pirate ships, old banks, a farmhouse under the floorboards, a train being robbed in a Western film. Writers still reach for it because it sounds solid and a little bit historical. You will also meet it in a stretched way: someone might say a place, or even a person's mind, is a strongbox, meaning nothing gets out of it. Note the spelling — one word, no space.

保險箱（可搬動的那種小鐵箱）。台灣人講到旅館房間或家裡那個，直接說「保險箱」就好；strongbox 帶點老派、故事裡的味道，像藏寶箱、錢箱那種。要注意：嵌在牆裡、大型的那種叫 safe（保險櫃），中文常常兩個都叫保險箱，英文卻分得比較開。