"unsoþfæstest" meaning in Old English

{
  "forms": [
    {
      "form": "sōþfæstest",
      "tags": [
        "canonical"
      ]
    }
  ],
  "lang": "Old English",
  "lang_code": "ang",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Old English 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"
        }
      ],
      "form_of": [
        {
          "word": "sōþfæst"
        }
      ],
      "glosses": [
        "superlative degree of sōþfæst"
      ],
      "id": "en-unsoþfæstest-ang-adj-FTFH-O1t",
      "links": [
        [
          "sōþfæst",
          "soþfæst#Old_English"
        ]
      ],
      "tags": [
        "form-of",
        "superlative"
      ]
    }
  ],
  "word": "unsoþfæstest"
}

{
  "forms": [
    {
      "form": "sōþfæstest",
      "tags": [
        "canonical"
      ]
    }
  ],
  "lang": "Old English",
  "lang_code": "ang",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "Old English entries with incorrect language header",
        "Old English non-lemma forms",
        "Old English superlative adjectives",
        "Pages with 1 entry"
      ],
      "form_of": [
        {
          "word": "sōþfæst"
        }
      ],
      "glosses": [
        "superlative degree of sōþfæst"
      ],
      "links": [
        [
          "sōþfæst",
          "soþfæst#Old_English"
        ]
      ],
      "tags": [
        "form-of",
        "superlative"
      ]
    }
  ],
  "word": "unsoþfæstest"
}