"I must say" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "I must say (not comparable)",
      "name": "en-adv"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
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          "source": "w"
        },
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          "kind": "other",
          "name": "English entries with language name categories using raw markup",
          "parents": [
            "Entries with language name categories using raw markup",
            "Entry maintenance"
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          "source": "w"
        },
        {
          "kind": "other",
          "name": "English sentences",
          "parents": [],
          "source": "w"
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          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
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          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1844, Benjamin Disraeli, Coningsby, etc, page 265",
          "text": "“I must say, I was very happy when I met Mr. Coningsby again at Cambridge,” said Lady Wallinger. “It gave me much greater pleasure than seeing any of the colleges.”",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A term of asseveration."
      ],
      "id": "en-I_must_say-en-adv-t-y4OVk9",
      "links": [
        [
          "asseveration",
          "asseveration#English"
        ]
      ],
      "synonyms": [
        {
          "word": "indeed"
        },
        {
          "word": "forsooth"
        },
        {
          "word": "in fact"
        },
        {
          "word": "as God is my witness"
        }
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "I must say"
}

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "I must say (not comparable)",
      "name": "en-adv"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        "English adverbs",
        "English entries with incorrect language header",
        "English entries with language name categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English sentences",
        "English terms with non-redundant non-automated sortkeys",
        "English terms with quotations",
        "English uncomparable adverbs"
      ],
      "examples": [
        {
          "ref": "1844, Benjamin Disraeli, Coningsby, etc, page 265",
          "text": "“I must say, I was very happy when I met Mr. Coningsby again at Cambridge,” said Lady Wallinger. “It gave me much greater pleasure than seeing any of the colleges.”",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A term of asseveration."
      ],
      "links": [
        [
          "asseveration",
          "asseveration#English"
        ]
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "indeed"
    },
    {
      "word": "forsooth"
    },
    {
      "word": "in fact"
    },
    {
      "word": "as God is my witness"
    }
  ],
  "word": "I must say"
}