"Hg" meaning in Conventions internationales

{
  "categories": [
    {
      "kind": "other",
      "name": "Compositions en grec ancien",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Mots en conventions internationales issus d’un mot en grec ancien",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Mots en conventions internationales issus d’un mot en latin",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Symboles en conventions internationales",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Conventions internationales",
      "orig": "conventions internationales",
      "parents": [],
      "source": "w"
    }
  ],
  "derived": [
    {
      "word": "mmHg"
    }
  ],
  "etymology_texts": [
    "Du latin hydrargyrus, lui-même issu du grec ancien ὑδράργυρος, hydrárguros, composé de ὕδωρ, hydor (« eau ») et de ἄργυρος, árguros (« argent »)."
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Symboles des éléments chimiques",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Symbole chimique du mercure."
      ],
      "id": "fr-Hg-conv-symbol-MmNGKKIu",
      "topics": [
        "chemistry"
      ]
    }
  ],
  "word": "Hg"
}

{
  "categories": [
    "Compositions en grec ancien",
    "Mots en conventions internationales issus d’un mot en grec ancien",
    "Mots en conventions internationales issus d’un mot en latin",
    "Symboles en conventions internationales",
    "conventions internationales"
  ],
  "derived": [
    {
      "word": "mmHg"
    }
  ],
  "etymology_texts": [
    "Du latin hydrargyrus, lui-même issu du grec ancien ὑδράργυρος, hydrárguros, composé de ὕδωρ, hydor (« eau ») et de ἄργυρος, árguros (« argent »)."
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "categories": [
        "Symboles des éléments chimiques"
      ],
      "glosses": [
        "Symbole chimique du mercure."
      ],
      "topics": [
        "chemistry"
      ]
    }
  ],
  "word": "Hg"
}