"extra-miler" meaning in English

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "extra mile",
        "3": "er",
        "id2": "occupation"
      },
      "expansion": "extra mile + -er",
      "name": "suffix"
    }
  ],
  "etymology_text": "From extra mile + -er.",
  "forms": [
    {
      "form": "extra-milers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "extra-miler (plural extra-milers)",
      "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"
        },
        {
          "kind": "other",
          "name": "English terms suffixed with -er (occupation)",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "One who goes the extra mile, or does more than is expected of them."
      ],
      "id": "en-extra-miler-en-noun-CmBWhFV-",
      "links": [
        [
          "goes the extra mile",
          "go the extra mile"
        ]
      ],
      "synonyms": [
        {
          "word": "extra miler"
        }
      ]
    }
  ],
  "word": "extra-miler"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "extra mile",
        "3": "er",
        "id2": "occupation"
      },
      "expansion": "extra mile + -er",
      "name": "suffix"
    }
  ],
  "etymology_text": "From extra mile + -er.",
  "forms": [
    {
      "form": "extra-milers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "extra-miler (plural extra-milers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English agent nouns",
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms suffixed with -er (occupation)",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "glosses": [
        "One who goes the extra mile, or does more than is expected of them."
      ],
      "links": [
        [
          "goes the extra mile",
          "go the extra mile"
        ]
      ]
    }
  ],
  "synonyms": [
    {
      "word": "extra miler"
    }
  ],
  "word": "extra-miler"
}