"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": "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 entries with language name categories using raw markup",
          "parents": [
            "Entries with language name categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms suffixed with -er (occupation)",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
          ],
          "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": "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 entries with language name categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms suffixed with -er (occupation)",
        "English terms with non-redundant non-automated sortkeys"
      ],
      "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"
}