"аркою" meaning in Russe

{
  "categories": [
    {
      "kind": "other",
      "name": "Formes de noms communs en russe",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Russe",
      "orig": "russe",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Russe",
  "lang_code": "ru",
  "pos": "noun",
  "pos_title": "Forme de nom commun",
  "raw_tags": [
    "féminin inanimé"
  ],
  "senses": [
    {
      "form_of": [
        {
          "word": "арка"
        }
      ],
      "glosses": [
        "Instrumental singulier de арка."
      ],
      "id": "fr-аркою-ru-noun-tb9SMDb6"
    }
  ],
  "tags": [
    "form-of"
  ],
  "word": "аркою"
}

{
  "categories": [
    "Formes de noms communs en russe",
    "russe"
  ],
  "lang": "Russe",
  "lang_code": "ru",
  "pos": "noun",
  "pos_title": "Forme de nom commun",
  "raw_tags": [
    "féminin inanimé"
  ],
  "senses": [
    {
      "form_of": [
        {
          "word": "арка"
        }
      ],
      "glosses": [
        "Instrumental singulier de арка."
      ]
    }
  ],
  "tags": [
    "form-of"
  ],
  "word": "аркою"
}