"treble-heading" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "treble-heading (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "langcode": "en",
          "name": "Rail transportation",
          "orig": "en:Rail transportation",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "bold_text_offsets": [
            [
              0,
              14
            ]
          ],
          "ref": "1962 November, “Motive power miscellany: Scottish Region”, in Modern Railways, page 354:",
          "text": "Treble-heading was again recorded on the Highland line on September 2 when the 3 p.m. and 5 p.m. from Inverness both passed Pitlochry with three Type 2 diesels.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "The use of three locomotives at the front, or head, of a train."
      ],
      "id": "en-treble-heading-en-noun-Enr8JvuO",
      "links": [
        [
          "rail transport",
          "rail transport"
        ]
      ],
      "raw_glosses": [
        "(rail transport) The use of three locomotives at the front, or head, of a train."
      ],
      "related": [
        {
          "word": "double-heading"
        }
      ],
      "tags": [
        "uncountable"
      ],
      "topics": [
        "rail-transport",
        "railways",
        "transport"
      ]
    }
  ],
  "word": "treble-heading"
}

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "treble-heading (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "double-heading"
    }
  ],
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "English uncountable nouns",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Rail transportation"
      ],
      "examples": [
        {
          "bold_text_offsets": [
            [
              0,
              14
            ]
          ],
          "ref": "1962 November, “Motive power miscellany: Scottish Region”, in Modern Railways, page 354:",
          "text": "Treble-heading was again recorded on the Highland line on September 2 when the 3 p.m. and 5 p.m. from Inverness both passed Pitlochry with three Type 2 diesels.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "The use of three locomotives at the front, or head, of a train."
      ],
      "links": [
        [
          "rail transport",
          "rail transport"
        ]
      ],
      "raw_glosses": [
        "(rail transport) The use of three locomotives at the front, or head, of a train."
      ],
      "tags": [
        "uncountable"
      ],
      "topics": [
        "rail-transport",
        "railways",
        "transport"
      ]
    }
  ],
  "word": "treble-heading"
}