"strong room" meaning in English

{
  "forms": [
    {
      "form": "strong rooms",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "strong room (plural strong rooms)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "strongroom"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1950 March, “Notes and News: Historic Documents Return to Euston”, in Railway Magazine, page 210:",
          "text": "Some 150,000 legal documents belonging to the London Midland Region of British Railways have recently made a journey in three railway vans from the strong room at Derby Station to be stored in the deed room in the Doric Arch at Euston, whence they were removed at the outbreak of war.",
          "type": "quote"
        }
      ],
      "glosses": [
        "Alternative spelling of strongroom."
      ],
      "id": "en-strong_room-en-noun-MlRCVmw5",
      "links": [
        [
          "strongroom",
          "strongroom#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "strong room"
}

{
  "forms": [
    {
      "form": "strong rooms",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "strong room (plural strong rooms)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "strongroom"
        }
      ],
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "examples": [
        {
          "ref": "1950 March, “Notes and News: Historic Documents Return to Euston”, in Railway Magazine, page 210:",
          "text": "Some 150,000 legal documents belonging to the London Midland Region of British Railways have recently made a journey in three railway vans from the strong room at Derby Station to be stored in the deed room in the Doric Arch at Euston, whence they were removed at the outbreak of war.",
          "type": "quote"
        }
      ],
      "glosses": [
        "Alternative spelling of strongroom."
      ],
      "links": [
        [
          "strongroom",
          "strongroom#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "strong room"
}