"icist" meaning in Ancien français

{
  "categories": [
    {
      "kind": "other",
      "name": "Formes d’adjectifs en ancien français",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Ancien français",
      "orig": "ancien français",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Ancien français",
  "lang_code": "fro",
  "pos": "adj",
  "pos_title": "Forme d’adjectif",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Exemples en ancien français",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "Psautier d’Oxford,édition de Francisque Michel, p. 29, circa 1100-50",
          "text": "Chi est icist reis de glorie ?",
          "translation": "Qui est ce roi de gloire ?"
        }
      ],
      "form_of": [
        {
          "word": "icest"
        }
      ],
      "glosses": [
        "Cas sujet, masculin singulier de icest."
      ],
      "id": "fr-icist-fro-adj-~djCXOdX"
    }
  ],
  "tags": [
    "form-of",
    "masculine"
  ],
  "word": "icist"
}

{
  "categories": [
    "Formes d’adjectifs en ancien français",
    "ancien français"
  ],
  "lang": "Ancien français",
  "lang_code": "fro",
  "pos": "adj",
  "pos_title": "Forme d’adjectif",
  "senses": [
    {
      "categories": [
        "Exemples en ancien français"
      ],
      "examples": [
        {
          "ref": "Psautier d’Oxford,édition de Francisque Michel, p. 29, circa 1100-50",
          "text": "Chi est icist reis de glorie ?",
          "translation": "Qui est ce roi de gloire ?"
        }
      ],
      "form_of": [
        {
          "word": "icest"
        }
      ],
      "glosses": [
        "Cas sujet, masculin singulier de icest."
      ]
    }
  ],
  "tags": [
    "form-of",
    "masculine"
  ],
  "word": "icist"
}