"einu" meaning in Icelandic

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "numeral form"
      },
      "expansion": "einu",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "num",
  "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 3 entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "_dis": "31 38 15 8 8",
          "kind": "other",
          "name": "Old Norse entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        },
        {
          "_dis": "42 50 5 1 2",
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w+disamb"
        }
      ],
      "form_of": [
        {
          "word": "einn"
        }
      ],
      "glosses": [
        "dative neuter singular of einn"
      ],
      "id": "en-einu-is-num-j2o65-pt",
      "links": [
        [
          "einn",
          "einn#Icelandic"
        ]
      ],
      "tags": [
        "dative",
        "form-of",
        "neuter",
        "singular"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ˈeiːnʏ/"
    },
    {
      "rhymes": "-eiːnʏ"
    }
  ],
  "word": "einu"
}

{
  "categories": [
    "Old Norse adjective forms",
    "Old Norse entries with incorrect language header",
    "Old Norse non-lemma forms",
    "Pages with 3 entries",
    "Pages with entries"
  ],
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "numeral form"
      },
      "expansion": "einu",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "num",
  "senses": [
    {
      "categories": [
        "Icelandic entries with incorrect language header",
        "Icelandic non-lemma forms",
        "Icelandic numeral forms",
        "Pages with 3 entries",
        "Pages with entries",
        "Rhymes:Icelandic/eiːnʏ",
        "Rhymes:Icelandic/eiːnʏ/2 syllables"
      ],
      "form_of": [
        {
          "word": "einn"
        }
      ],
      "glosses": [
        "dative neuter singular of einn"
      ],
      "links": [
        [
          "einn",
          "einn#Icelandic"
        ]
      ],
      "tags": [
        "dative",
        "form-of",
        "neuter",
        "singular"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ˈeiːnʏ/"
    },
    {
      "rhymes": "-eiːnʏ"
    }
  ],
  "word": "einu"
}