A strongroom is a whole room built to keep valuable things safe — thick walls, a heavy door, usually a lock that only a few people can open. Banks have them; so do jewellers, museums, big hotels, and sometimes government offices holding documents. Think of the room the robbers try to get into in a film: that is the strongroom. It is British English mostly; Americans are more likely to say 'vault', and 'vault' is now common everywhere, including in British newspapers. If you want one word people will always understand, use vault. Strongroom is a little plainer and more everyday-British — a shop's back room where the good stock is locked up can be called the strongroom without sounding dramatic. One word, no space, and it does not take a hyphen in modern writing.

金庫、保險庫（銀行或店裡那間鎖起來的房間）。台灣新聞講銀行那種多半說「金庫」。英式英文用 strongroom，美式和現在的通用說法是 vault，想保險就用 vault。