"fm" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Symboles en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Lexique en anglais de la métrologie",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Symbole du fathom (la brasse en français), unité de mesure de profondeur hydrographique."
      ],
      "id": "fr-fm-en-symbol-FObliV8s",
      "topics": [
        "metrology"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ˈfæð.əm\\"
    }
  ],
  "word": "fm"
}

{
  "categories": [
    "Symboles en anglais",
    "anglais"
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "categories": [
        "Lexique en anglais de la métrologie"
      ],
      "glosses": [
        "Symbole du fathom (la brasse en français), unité de mesure de profondeur hydrographique."
      ],
      "topics": [
        "metrology"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "\\ˈfæð.əm\\"
    }
  ],
  "word": "fm"
}