"five-nine" meaning in English

{
  "forms": [
    {
      "form": "five-nines",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "five-nine (plural five-nines)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1917, Wilfred Owen, Dulce Et Decorum Est",
          "text": "All went lame; all blind; / Drunk with fatigue; deaf even to the hoots / Of tired, outstripped Five-Nines that dropped behind.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A 5.9-inch artillery shell of the kind used by Germany in World War I."
      ],
      "id": "en-five-nine-en-noun-bhXquvdA",
      "links": [
        [
          "artillery",
          "artillery"
        ],
        [
          "shell",
          "shell"
        ]
      ],
      "raw_glosses": [
        "(historical) A 5.9-inch artillery shell of the kind used by Germany in World War I."
      ],
      "tags": [
        "historical"
      ]
    }
  ],
  "word": "five-nine"
}

{
  "forms": [
    {
      "form": "five-nines",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "five-nine (plural five-nines)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with historical senses",
        "English terms with quotations",
        "Quotation templates to be cleaned"
      ],
      "examples": [
        {
          "ref": "1917, Wilfred Owen, Dulce Et Decorum Est",
          "text": "All went lame; all blind; / Drunk with fatigue; deaf even to the hoots / Of tired, outstripped Five-Nines that dropped behind.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "A 5.9-inch artillery shell of the kind used by Germany in World War I."
      ],
      "links": [
        [
          "artillery",
          "artillery"
        ],
        [
          "shell",
          "shell"
        ]
      ],
      "raw_glosses": [
        "(historical) A 5.9-inch artillery shell of the kind used by Germany in World War I."
      ],
      "tags": [
        "historical"
      ]
    }
  ],
  "word": "five-nine"
}