"брѣзьнъ" meaning in Vieux slave

{
  "categories": [
    {
      "kind": "other",
      "name": "Calendrier en vieux slave",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Noms communs en vieux slave",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Vieux slave",
      "orig": "vieux slave",
      "parents": [],
      "source": "w"
    }
  ],
  "derived": [
    {
      "lang": "Tchèque",
      "lang_code": "cs",
      "word": "březen"
    }
  ],
  "etymology_texts": [
    "De брѣза brěza et -ьнъ : c’est le mois quand éclosent les bourgeons des bouleaux → voir germinal."
  ],
  "lang": "Vieux slave",
  "lang_code": "cu",
  "pos": "noun",
  "pos_title": "Nom commun",
  "senses": [
    {
      "glosses": [
        "Avril."
      ],
      "id": "fr-брѣзьнъ-cu-noun-boaB~IwE"
    }
  ],
  "tags": [
    "masculine"
  ],
  "word": "брѣзьнъ"
}

{
  "categories": [
    "Calendrier en vieux slave",
    "Noms communs en vieux slave",
    "vieux slave"
  ],
  "derived": [
    {
      "lang": "Tchèque",
      "lang_code": "cs",
      "word": "březen"
    }
  ],
  "etymology_texts": [
    "De брѣза brěza et -ьнъ : c’est le mois quand éclosent les bourgeons des bouleaux → voir germinal."
  ],
  "lang": "Vieux slave",
  "lang_code": "cu",
  "pos": "noun",
  "pos_title": "Nom commun",
  "senses": [
    {
      "glosses": [
        "Avril."
      ]
    }
  ],
  "tags": [
    "masculine"
  ],
  "word": "брѣзьнъ"
}