"不知火" meaning in 日本語

{
  "categories": [
    {
      "kind": "other",
      "name": "日本語",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "日本語 和語の漢字表記",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "熟字訓",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "日本語",
  "lang_code": "ja",
  "pos": "unknown",
  "pos_title": "和語の漢字表記",
  "senses": [
    {
      "form_of": [
        {
          "word": "自然現象の呼称等"
        }
      ],
      "glosses": [
        "海上に無数の火影が浮いて見える自然現象の呼称等。詳細は しらぬい を参照。"
      ],
      "id": "ja-不知火-ja-unknown-kvHBho12"
    }
  ],
  "tags": [
    "form-of",
    "kanji"
  ],
  "word": "不知火"
}

{
  "categories": [
    "日本語",
    "日本語 和語の漢字表記",
    "熟字訓"
  ],
  "lang": "日本語",
  "lang_code": "ja",
  "pos": "unknown",
  "pos_title": "和語の漢字表記",
  "senses": [
    {
      "form_of": [
        {
          "word": "自然現象の呼称等"
        }
      ],
      "glosses": [
        "海上に無数の火影が浮いて見える自然現象の呼称等。詳細は しらぬい を参照。"
      ]
    }
  ],
  "tags": [
    "form-of",
    "kanji"
  ],
  "word": "不知火"
}