"thitherto" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Adverbes en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Lemmes en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "adv",
  "pos_title": "Adverbe",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Exemples en anglais",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Exemples en anglais à traduire",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Termes vieillis en anglais",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "He brought back to England potatoes, thitherto completely unkown in his homeland."
        }
      ],
      "glosses": [
        "jusqu'alors"
      ],
      "id": "fr-thitherto-en-adv-n9Vclp6m",
      "tags": [
        "dated"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "thereto"
    },
    {
      "word": "then"
    },
    {
      "word": "thus far"
    }
  ],
  "word": "thitherto"
}

{
  "categories": [
    "Adverbes en anglais",
    "Lemmes en anglais",
    "anglais"
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "adv",
  "pos_title": "Adverbe",
  "senses": [
    {
      "categories": [
        "Exemples en anglais",
        "Exemples en anglais à traduire",
        "Termes vieillis en anglais"
      ],
      "examples": [
        {
          "text": "He brought back to England potatoes, thitherto completely unkown in his homeland."
        }
      ],
      "glosses": [
        "jusqu'alors"
      ],
      "tags": [
        "dated"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "thereto"
    },
    {
      "word": "then"
    },
    {
      "word": "thus far"
    }
  ],
  "word": "thitherto"
}