"M6" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Lemmes en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Noms communs en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "Initiale de motorway « autoroute »."
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Nom commun",
  "senses": [
    {
      "glosses": [
        "Autoroute numéro six."
      ],
      "id": "fr-M6-en-noun-bO0h2PRN"
    },
    {
      "categories": [
        {
          "kind": "other",
          "name": "Anglais du Royaume-Uni",
          "orig": "anglais du Royaume-Uni",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Autoroute reliant Rugby à Carlisle."
      ],
      "id": "fr-M6-en-noun-e-PdWTm2",
      "raw_tags": [
        "Royaume-Uni"
      ],
      "tags": [
        "especially"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ɜmˈsɪks\\"
    }
  ],
  "tags": [
    "invariable"
  ],
  "word": "M6"
}

{
  "categories": [
    "Lemmes en anglais",
    "Noms communs en anglais",
    "anglais"
  ],
  "etymology_texts": [
    "Initiale de motorway « autoroute »."
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Nom commun",
  "senses": [
    {
      "glosses": [
        "Autoroute numéro six."
      ]
    },
    {
      "categories": [
        "anglais du Royaume-Uni"
      ],
      "glosses": [
        "Autoroute reliant Rugby à Carlisle."
      ],
      "raw_tags": [
        "Royaume-Uni"
      ],
      "tags": [
        "especially"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ɜmˈsɪks\\"
    }
  ],
  "tags": [
    "invariable"
  ],
  "word": "M6"
}