"nuclear meltdown" meaning in English

{
  "forms": [
    {
      "form": "nuclear meltdowns",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
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      "args": {},
      "expansion": "nuclear meltdown (plural nuclear meltdowns)",
      "name": "en-noun"
    }
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
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          "parents": [],
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        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Radioactivity",
          "orig": "en:Radioactivity",
          "parents": [
            "Nuclear physics",
            "Radiation",
            "Physics",
            "Quantum mechanics",
            "Energy",
            "Sciences",
            "Nature",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A severe nuclear reactor accident that results in core damage from overheating"
      ],
      "id": "en-nuclear_meltdown-en-noun-UwDB1izv",
      "links": [
        [
          "nuclear reactor",
          "nuclear reactor"
        ],
        [
          "core",
          "core"
        ],
        [
          "damage",
          "damage"
        ],
        [
          "overheating",
          "overheating"
        ]
      ],
      "translations": [
        {
          "code": "de",
          "lang": "German",
          "sense": "severe nuclear reactor accident",
          "tags": [
            "feminine"
          ],
          "word": "Kernschmelze"
        },
        {
          "code": "es",
          "lang": "Spanish",
          "sense": "severe nuclear reactor accident",
          "tags": [
            "feminine"
          ],
          "word": "fusión de núcleo"
        }
      ],
      "wikipedia": [
        "nuclear meltdown"
      ]
    }
  ],
  "word": "nuclear meltdown"
}

{
  "forms": [
    {
      "form": "nuclear meltdowns",
      "tags": [
        "plural"
      ]
    }
  ],
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      "expansion": "nuclear meltdown (plural nuclear meltdowns)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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        "Terms with German translations",
        "Terms with Spanish translations",
        "en:Radioactivity"
      ],
      "glosses": [
        "A severe nuclear reactor accident that results in core damage from overheating"
      ],
      "links": [
        [
          "nuclear reactor",
          "nuclear reactor"
        ],
        [
          "core",
          "core"
        ],
        [
          "damage",
          "damage"
        ],
        [
          "overheating",
          "overheating"
        ]
      ],
      "wikipedia": [
        "nuclear meltdown"
      ]
    }
  ],
  "translations": [
    {
      "code": "de",
      "lang": "German",
      "sense": "severe nuclear reactor accident",
      "tags": [
        "feminine"
      ],
      "word": "Kernschmelze"
    },
    {
      "code": "es",
      "lang": "Spanish",
      "sense": "severe nuclear reactor accident",
      "tags": [
        "feminine"
      ],
      "word": "fusión de núcleo"
    }
  ],
  "word": "nuclear meltdown"
}