"could have sworn" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "verb"
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      "expansion": "could have sworn",
      "name": "head"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
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          "source": "w"
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      ],
      "examples": [
        {
          "text": "\"You lost your bracelet?\" \"Yeah, but I could have sworn it was in the kitchen on the table when I last saw it.\""
        }
      ],
      "glosses": [
        "Is very sure about; especially when the thing in question is apparently not the case or could be doubted."
      ],
      "id": "en-could_have_sworn-en-verb-lcYMGUV0",
      "links": [
        [
          "sure",
          "sure#English"
        ]
      ],
      "raw_glosses": [
        "(informal) Is very sure about; especially when the thing in question is apparently not the case or could be doubted."
      ],
      "synonyms": [
        {
          "word": "could've sworn"
        }
      ],
      "tags": [
        "informal"
      ]
    }
  ],
  "word": "could have sworn"
}

{
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "verb"
      },
      "expansion": "could have sworn",
      "name": "head"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English informal terms",
        "English lemmas",
        "English multiword terms",
        "English verbs"
      ],
      "examples": [
        {
          "text": "\"You lost your bracelet?\" \"Yeah, but I could have sworn it was in the kitchen on the table when I last saw it.\""
        }
      ],
      "glosses": [
        "Is very sure about; especially when the thing in question is apparently not the case or could be doubted."
      ],
      "links": [
        [
          "sure",
          "sure#English"
        ]
      ],
      "raw_glosses": [
        "(informal) Is very sure about; especially when the thing in question is apparently not the case or could be doubted."
      ],
      "tags": [
        "informal"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "could've sworn"
    }
  ],
  "word": "could have sworn"
}