"fjallahéröðum" meaning in Icelandic

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "noun form"
      },
      "expansion": "fjallahéröðum",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Icelandic 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"
        }
      ],
      "form_of": [
        {
          "word": "fjallahérað"
        }
      ],
      "glosses": [
        "indefinite dative plural of fjallahérað"
      ],
      "id": "en-fjallahéröðum-is-noun-ikFU~VAO",
      "links": [
        [
          "fjallahérað",
          "fjallahérað#Icelandic"
        ]
      ],
      "tags": [
        "dative",
        "form-of",
        "indefinite",
        "plural"
      ]
    }
  ],
  "word": "fjallahéröðum"
}

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "noun form"
      },
      "expansion": "fjallahéröðum",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Icelandic entries with incorrect language header",
        "Icelandic non-lemma forms",
        "Icelandic noun forms",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "form_of": [
        {
          "word": "fjallahérað"
        }
      ],
      "glosses": [
        "indefinite dative plural of fjallahérað"
      ],
      "links": [
        [
          "fjallahérað",
          "fjallahérað#Icelandic"
        ]
      ],
      "tags": [
        "dative",
        "form-of",
        "indefinite",
        "plural"
      ]
    }
  ],
  "word": "fjallahéröðum"
}