"seissed" meaning in Middle Irish

{
  "descendants": [
    {
      "depth": 1,
      "templates": [
        {
          "args": {
            "1": "ga",
            "2": "seiseadh"
          },
          "expansion": "Irish: seiseadh",
          "name": "desc"
        }
      ],
      "text": "Irish: seiseadh"
    },
    {
      "depth": 1,
      "templates": [
        {
          "args": {
            "1": "gd",
            "2": "seiseadh"
          },
          "expansion": "Scottish Gaelic: seiseadh",
          "name": "desc"
        }
      ],
      "text": "Scottish Gaelic: seiseadh"
    }
  ],
  "etymology_templates": [
    {
      "args": {
        "1": "mga",
        "2": "sga",
        "3": "seissed"
      },
      "expansion": "Old Irish seissed",
      "name": "inh"
    }
  ],
  "etymology_text": "From Old Irish seissed.",
  "forms": [
    {
      "form": "no-table-tags",
      "source": "mutation",
      "tags": [
        "table-tags"
      ]
    },
    {
      "form": "mga-mutation",
      "source": "mutation",
      "tags": [
        "inflection-template"
      ]
    },
    {
      "form": "seissed",
      "source": "mutation",
      "tags": [
        "mutation",
        "mutation-radical"
      ]
    },
    {
      "form": "ṡeissed",
      "source": "mutation",
      "tags": [
        "lenition",
        "mutation"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "mga",
        "2": "adjective",
        "cat2": "ordinal numbers"
      },
      "expansion": "seissed",
      "name": "head"
    }
  ],
  "inflection_templates": [
    {
      "args": {
        "1": "s",
        "2": "eissed"
      },
      "name": "mga-mutation"
    }
  ],
  "lang": "Middle Irish",
  "lang_code": "mga",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Middle Irish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Middle Irish links with redundant target parameters",
          "parents": [
            "Links with redundant target parameters",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "name": "Middle Irish ordinal numbers",
          "parents": [
            "Ordinal numbers",
            "Numbers",
            "All topics",
            "Terms by semantic function",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "sixth"
      ],
      "id": "en-seissed-mga-adj-7~qmjSjf",
      "links": [
        [
          "sixth",
          "sixth"
        ]
      ],
      "synonyms": [
        {
          "word": "seised"
        },
        {
          "word": "sesed"
        },
        {
          "word": "sessed"
        }
      ]
    }
  ],
  "word": "seissed"
}

{
  "descendants": [
    {
      "depth": 1,
      "templates": [
        {
          "args": {
            "1": "ga",
            "2": "seiseadh"
          },
          "expansion": "Irish: seiseadh",
          "name": "desc"
        }
      ],
      "text": "Irish: seiseadh"
    },
    {
      "depth": 1,
      "templates": [
        {
          "args": {
            "1": "gd",
            "2": "seiseadh"
          },
          "expansion": "Scottish Gaelic: seiseadh",
          "name": "desc"
        }
      ],
      "text": "Scottish Gaelic: seiseadh"
    }
  ],
  "etymology_templates": [
    {
      "args": {
        "1": "mga",
        "2": "sga",
        "3": "seissed"
      },
      "expansion": "Old Irish seissed",
      "name": "inh"
    }
  ],
  "etymology_text": "From Old Irish seissed.",
  "forms": [
    {
      "form": "no-table-tags",
      "source": "mutation",
      "tags": [
        "table-tags"
      ]
    },
    {
      "form": "mga-mutation",
      "source": "mutation",
      "tags": [
        "inflection-template"
      ]
    },
    {
      "form": "seissed",
      "source": "mutation",
      "tags": [
        "mutation",
        "mutation-radical"
      ]
    },
    {
      "form": "ṡeissed",
      "source": "mutation",
      "tags": [
        "lenition",
        "mutation"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "mga",
        "2": "adjective",
        "cat2": "ordinal numbers"
      },
      "expansion": "seissed",
      "name": "head"
    }
  ],
  "inflection_templates": [
    {
      "args": {
        "1": "s",
        "2": "eissed"
      },
      "name": "mga-mutation"
    }
  ],
  "lang": "Middle Irish",
  "lang_code": "mga",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "Middle Irish adjectives",
        "Middle Irish entries with incorrect language header",
        "Middle Irish lemmas",
        "Middle Irish links with redundant target parameters",
        "Middle Irish ordinal numbers",
        "Middle Irish terms derived from Old Irish",
        "Middle Irish terms inherited from Old Irish"
      ],
      "glosses": [
        "sixth"
      ],
      "links": [
        [
          "sixth",
          "sixth"
        ]
      ]
    }
  ],
  "synonyms": [
    {
      "word": "seised"
    },
    {
      "word": "sesed"
    },
    {
      "word": "sessed"
    }
  ],
  "word": "seissed"
}