"a1" meaning in English

{
  "etymology_text": "The symbol used for a first-class vessel in Lloyd's Register of Shipping.",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "a1 (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "glosses": [
        "first rate or excellent"
      ],
      "id": "en-a1-en-adj-os-4tSRx",
      "tags": [
        "not-comparable"
      ]
    },
    {
      "categories": [
        {
          "_dis": "7 93",
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        }
      ],
      "glosses": [
        "in first class condition"
      ],
      "id": "en-a1-en-adj-Chbfl~4z",
      "raw_glosses": [
        "(of a ship) in first class condition"
      ],
      "raw_tags": [
        "of a ship"
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "a1"
}

{
  "categories": [
    "English adjectives",
    "English entries with incorrect language header",
    "English lemmas",
    "English terms spelled with numbers",
    "English uncomparable adjectives"
  ],
  "etymology_text": "The symbol used for a first-class vessel in Lloyd's Register of Shipping.",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "a1 (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "glosses": [
        "first rate or excellent"
      ],
      "tags": [
        "not-comparable"
      ]
    },
    {
      "glosses": [
        "in first class condition"
      ],
      "raw_glosses": [
        "(of a ship) in first class condition"
      ],
      "raw_tags": [
        "of a ship"
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "a1"
}