"herja" meaning in Icelandic

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "noun form"
      },
      "expansion": "herja",
      "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"
        },
        {
          "_dis": "2 17 3 12 17 1 4 1 15 2 2 16 6 2",
          "kind": "other",
          "name": "Old Norse entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        }
      ],
      "form_of": [
        {
          "word": "her"
        }
      ],
      "glosses": [
        "indefinite genitive plural of her"
      ],
      "id": "en-herja-is-noun-B~gdEr2O",
      "links": [
        [
          "her",
          "her#Icelandic"
        ]
      ],
      "tags": [
        "form-of",
        "genitive",
        "indefinite",
        "plural"
      ]
    }
  ],
  "word": "herja"
}

{
  "categories": [
    "Old Norse class 2 weak verbs",
    "Old Norse entries with incorrect language header",
    "Old Norse lemmas",
    "Old Norse terms derived from Proto-Germanic",
    "Old Norse terms inherited from Proto-Germanic",
    "Old Norse verbs"
  ],
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "noun form"
      },
      "expansion": "herja",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Icelandic entries with incorrect language header",
        "Icelandic non-lemma forms",
        "Icelandic noun forms"
      ],
      "form_of": [
        {
          "word": "her"
        }
      ],
      "glosses": [
        "indefinite genitive plural of her"
      ],
      "links": [
        [
          "her",
          "her#Icelandic"
        ]
      ],
      "tags": [
        "form-of",
        "genitive",
        "indefinite",
        "plural"
      ]
    }
  ],
  "word": "herja"
}