"рѣкы" meaning in Vieux slave

{
  "categories": [
    {
      "kind": "other",
      "name": "Formes de noms communs en vieux slave",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Vieux slave",
      "orig": "vieux slave",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Vieux slave",
  "lang_code": "cu",
  "pos": "noun",
  "pos_title": "Forme de nom commun",
  "senses": [
    {
      "form_of": [
        {
          "word": "рѣка"
        }
      ],
      "glosses": [
        "Génitif singulier de рѣка."
      ],
      "id": "fr-рѣкы-cu-noun-oEGrT60a"
    }
  ],
  "tags": [
    "form-of"
  ],
  "word": "рѣкы"
}

{
  "categories": [
    "Formes de noms communs en vieux slave",
    "vieux slave"
  ],
  "lang": "Vieux slave",
  "lang_code": "cu",
  "pos": "noun",
  "pos_title": "Forme de nom commun",
  "senses": [
    {
      "form_of": [
        {
          "word": "рѣка"
        }
      ],
      "glosses": [
        "Génitif singulier de рѣка."
      ]
    }
  ],
  "tags": [
    "form-of"
  ],
  "word": "рѣкы"
}