"песъ" meaning in Old East Slavic

{
  "forms": [
    {
      "form": "pesŭ",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "orv",
        "2": "noun",
        "g": "m"
      },
      "expansion": "песъ (pesŭ) m",
      "name": "head"
    }
  ],
  "lang": "Old East Slavic",
  "lang_code": "orv",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "extra": "pĭsŭ",
          "word": "пьсъ"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Old East Slavic entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Old East Slavic entries with topic categories using raw markup",
          "parents": [
            "Entries with topic categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "lifeform",
          "langcode": "orv",
          "name": "Canids",
          "orig": "orv:Canids",
          "parents": [
            "Carnivores",
            "Mammals",
            "Vertebrates",
            "Chordates",
            "Animals",
            "Lifeforms",
            "All topics",
            "Life",
            "Fundamental",
            "Nature"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Alternative form of пьсъ (pĭsŭ)"
      ],
      "id": "en-песъ-orv-noun-VKcJLZzq",
      "links": [
        [
          "пьсъ",
          "пьсъ#Old East Slavic"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "masculine"
      ]
    }
  ],
  "word": "песъ"
}

{
  "forms": [
    {
      "form": "pesŭ",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "orv",
        "2": "noun",
        "g": "m"
      },
      "expansion": "песъ (pesŭ) m",
      "name": "head"
    }
  ],
  "lang": "Old East Slavic",
  "lang_code": "orv",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "extra": "pĭsŭ",
          "word": "пьсъ"
        }
      ],
      "categories": [
        "Old East Slavic entries with incorrect language header",
        "Old East Slavic entries with topic categories using raw markup",
        "Old East Slavic lemmas",
        "Old East Slavic masculine nouns",
        "Old East Slavic nouns",
        "orv:Canids"
      ],
      "glosses": [
        "Alternative form of пьсъ (pĭsŭ)"
      ],
      "links": [
        [
          "пьсъ",
          "пьсъ#Old East Slavic"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "masculine"
      ]
    }
  ],
  "word": "песъ"
}