"съ" meaning in Bulgarian

{
  "head_templates": [
    {
      "args": {
        "1": "bg",
        "2": "preposition"
      },
      "expansion": "съ • (s)",
      "name": "head"
    }
  ],
  "lang": "Bulgarian",
  "lang_code": "bg",
  "pos": "prep",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Bulgarian entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Bulgarian pre-1945 spellings",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Bulgarian prepositions",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 3 entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Pre-1945 spelling of с (s)."
      ],
      "id": "en-съ-bg-prep-0X7ULMn6",
      "links": [
        [
          "с",
          "с#Bulgarian"
        ]
      ],
      "raw_glosses": [
        "(obsolete) Pre-1945 spelling of с (s)."
      ],
      "tags": [
        "obsolete"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "[s]"
    }
  ],
  "word": "съ"
}

{
  "head_templates": [
    {
      "args": {
        "1": "bg",
        "2": "preposition"
      },
      "expansion": "съ • (s)",
      "name": "head"
    }
  ],
  "lang": "Bulgarian",
  "lang_code": "bg",
  "pos": "prep",
  "senses": [
    {
      "categories": [
        "Bulgarian entries with incorrect language header",
        "Bulgarian lemmas",
        "Bulgarian obsolete forms",
        "Bulgarian pre-1945 spellings",
        "Bulgarian prepositions",
        "Bulgarian terms with IPA pronunciation",
        "Bulgarian terms with obsolete senses",
        "Pages with 3 entries",
        "Pages with entries"
      ],
      "glosses": [
        "Pre-1945 spelling of с (s)."
      ],
      "links": [
        [
          "с",
          "с#Bulgarian"
        ]
      ],
      "raw_glosses": [
        "(obsolete) Pre-1945 spelling of с (s)."
      ],
      "tags": [
        "obsolete"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "[s]"
    }
  ],
  "word": "съ"
}