"MsTh" meaning in Conventions internationales

{
  "categories": [
    {
      "kind": "other",
      "name": "Symboles désuets des éléments chimiques",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Symboles en conventions internationales",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Conventions internationales",
      "orig": "conventions internationales",
      "parents": [],
      "source": "w"
    }
  ],
  "hyponyms": [
    {
      "word": "MsThᴵ"
    },
    {
      "word": "MsTh₁"
    },
    {
      "word": "MsThᴵᴵ"
    },
    {
      "word": "MsTh₂"
    }
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "glosses": [
        "Symbole du mésothorium, dont on distinguait deux espèces (mésothorium I et II)."
      ],
      "id": "fr-MsTh-conv-symbol-LsJOxg38",
      "tags": [
        "obsolete"
      ],
      "topics": [
        "chemistry"
      ]
    }
  ],
  "tags": [
    "invariable"
  ],
  "word": "MsTh"
}

{
  "categories": [
    "Symboles désuets des éléments chimiques",
    "Symboles en conventions internationales",
    "conventions internationales"
  ],
  "hyponyms": [
    {
      "word": "MsThᴵ"
    },
    {
      "word": "MsTh₁"
    },
    {
      "word": "MsThᴵᴵ"
    },
    {
      "word": "MsTh₂"
    }
  ],
  "lang": "Conventions internationales",
  "lang_code": "conv",
  "pos": "symbol",
  "pos_title": "Symbole",
  "senses": [
    {
      "glosses": [
        "Symbole du mésothorium, dont on distinguait deux espèces (mésothorium I et II)."
      ],
      "tags": [
        "obsolete"
      ],
      "topics": [
        "chemistry"
      ]
    }
  ],
  "tags": [
    "invariable"
  ],
  "word": "MsTh"
}