"the double O" meaning in English

{
  "etymology_text": "By visual analogy with a pair of eyes or spectacles.",
  "head_templates": [
    {
      "args": {
        "1": "!"
      },
      "expansion": "the double O (plural not attested)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "American English",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English nouns with unattested plurals",
          "parents": [
            "Nouns with unattested plurals",
            "Nouns",
            "Lemmas"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1916, Ring W. Lardner, “Three Kings and a Pair”, in The Saturday Evening Post",
          "text": "So then I and Bishop knocked the street-car service and President Wilson and give each other the double O.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A thorough look or inspection."
      ],
      "id": "en-the_double_O-en-noun-4QHcygar",
      "raw_glosses": [
        "(obsolete, US, slang) A thorough look or inspection."
      ],
      "synonyms": [
        {
          "word": "the double o"
        },
        {
          "word": "the double-O"
        },
        {
          "word": "the double-o"
        }
      ],
      "tags": [
        "US",
        "no-plural",
        "obsolete",
        "slang"
      ]
    }
  ],
  "word": "the double O"
}

{
  "etymology_text": "By visual analogy with a pair of eyes or spectacles.",
  "head_templates": [
    {
      "args": {
        "1": "!"
      },
      "expansion": "the double O (plural not attested)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "American English",
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English nouns with unattested plurals",
        "English slang",
        "English terms with obsolete senses",
        "English terms with quotations"
      ],
      "examples": [
        {
          "ref": "1916, Ring W. Lardner, “Three Kings and a Pair”, in The Saturday Evening Post",
          "text": "So then I and Bishop knocked the street-car service and President Wilson and give each other the double O.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A thorough look or inspection."
      ],
      "raw_glosses": [
        "(obsolete, US, slang) A thorough look or inspection."
      ],
      "tags": [
        "US",
        "no-plural",
        "obsolete",
        "slang"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "the double o"
    },
    {
      "word": "the double-O"
    },
    {
      "word": "the double-o"
    }
  ],
  "word": "the double O"
}