"чём" meaning in Russian

{
  "forms": [
    {
      "form": "čom",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "ru",
        "2": "pronoun form"
      },
      "expansion": "чём • (čom)",
      "name": "head"
    }
  ],
  "lang": "Russian",
  "lang_code": "ru",
  "pos": "pron",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Russian entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "english": "What on earth are you arguing about?",
          "roman": "O čom že vy spórite?",
          "text": "О чём же вы спо́рите?",
          "type": "example"
        }
      ],
      "form_of": [
        {
          "extra": "što",
          "word": "что"
        }
      ],
      "glosses": [
        "prepositional of что (što)"
      ],
      "id": "en-чём-ru-pron-E-k1n4l~",
      "links": [
        [
          "что",
          "что#Russian"
        ]
      ],
      "related": [
        {
          "roman": "čem",
          "word": "чем"
        }
      ],
      "synonyms": [
        {
          "roman": "čem",
          "word": "чемъ"
        },
        {
          "roman": "čom",
          "word": "чёмъ — Pre-reform orthography (1918)"
        }
      ],
      "tags": [
        "form-of",
        "prepositional"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "[t͡ɕɵm]"
    }
  ],
  "word": "чём"
}

{
  "forms": [
    {
      "form": "čom",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "ru",
        "2": "pronoun form"
      },
      "expansion": "чём • (čom)",
      "name": "head"
    }
  ],
  "lang": "Russian",
  "lang_code": "ru",
  "pos": "pron",
  "related": [
    {
      "roman": "čem",
      "word": "чем"
    }
  ],
  "senses": [
    {
      "categories": [
        "Russian 1-syllable words",
        "Russian entries with incorrect language header",
        "Russian non-lemma forms",
        "Russian pronoun forms",
        "Russian terms with IPA pronunciation",
        "Russian terms with usage examples"
      ],
      "examples": [
        {
          "english": "What on earth are you arguing about?",
          "roman": "O čom že vy spórite?",
          "text": "О чём же вы спо́рите?",
          "type": "example"
        }
      ],
      "form_of": [
        {
          "extra": "što",
          "word": "что"
        }
      ],
      "glosses": [
        "prepositional of что (što)"
      ],
      "links": [
        [
          "что",
          "что#Russian"
        ]
      ],
      "tags": [
        "form-of",
        "prepositional"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "[t͡ɕɵm]"
    }
  ],
  "synonyms": [
    {
      "roman": "čem",
      "word": "чемъ"
    },
    {
      "roman": "čom",
      "word": "чёмъ — Pre-reform orthography (1918)"
    }
  ],
  "word": "чём"
}