"þat" meaning in Icelandic

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "pronoun",
        "g": "n"
      },
      "expansion": "þat n",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "pron",
  "senses": [
    {
      "alt_of": [
        {
          "word": "það"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Icelandic entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Icelandic pronouns",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Obsolete spelling of það"
      ],
      "id": "en-þat-is-pron-ADM0SvOL",
      "links": [
        [
          "það",
          "það#Icelandic"
        ]
      ],
      "tags": [
        "alt-of",
        "neuter",
        "obsolete"
      ]
    }
  ],
  "word": "þat"
}

{
  "categories": [
    "Old Norse entries with incorrect language header",
    "Old Norse non-lemma forms",
    "Old Norse pronoun forms",
    "Old Norse terms derived from Proto-Germanic",
    "Old Norse terms derived from Proto-Indo-European",
    "Old Norse terms inherited from Proto-Germanic",
    "Old Norse terms inherited from Proto-Indo-European"
  ],
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "pronoun",
        "g": "n"
      },
      "expansion": "þat n",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "pron",
  "senses": [
    {
      "alt_of": [
        {
          "word": "það"
        }
      ],
      "categories": [
        "Icelandic entries with incorrect language header",
        "Icelandic lemmas",
        "Icelandic obsolete forms",
        "Icelandic pronouns"
      ],
      "glosses": [
        "Obsolete spelling of það"
      ],
      "links": [
        [
          "það",
          "það#Icelandic"
        ]
      ],
      "tags": [
        "alt-of",
        "neuter",
        "obsolete"
      ]
    }
  ],
  "word": "þat"
}