"vanishing twin" meaning in English

{
  "forms": [
    {
      "form": "vanishing twins",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "vanishing twin (plural vanishing twins)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Siblings",
          "orig": "en:Siblings",
          "parents": [
            "Family members",
            "Family",
            "People",
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A fetus in a multigestation pregnancy that dies in utero and is then partially or completely reabsorbed by its twin."
      ],
      "id": "en-vanishing_twin-en-noun-FjvSLD1g",
      "links": [
        [
          "fetus",
          "fetus"
        ],
        [
          "multigestation",
          "multigestation"
        ],
        [
          "pregnancy",
          "pregnancy"
        ],
        [
          "die",
          "die"
        ],
        [
          "in utero",
          "in utero"
        ],
        [
          "reabsorb",
          "reabsorb"
        ]
      ],
      "related": [
        {
          "word": "fetus papyraceus"
        }
      ],
      "wikipedia": [
        "vanishing twin"
      ]
    }
  ],
  "word": "vanishing twin"
}

{
  "forms": [
    {
      "form": "vanishing twins",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "vanishing twin (plural vanishing twins)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "fetus papyraceus"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "en:Siblings"
      ],
      "glosses": [
        "A fetus in a multigestation pregnancy that dies in utero and is then partially or completely reabsorbed by its twin."
      ],
      "links": [
        [
          "fetus",
          "fetus"
        ],
        [
          "multigestation",
          "multigestation"
        ],
        [
          "pregnancy",
          "pregnancy"
        ],
        [
          "die",
          "die"
        ],
        [
          "in utero",
          "in utero"
        ],
        [
          "reabsorb",
          "reabsorb"
        ]
      ],
      "wikipedia": [
        "vanishing twin"
      ]
    }
  ],
  "word": "vanishing twin"
}