"undreamed-of" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Adjectifs en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Lemmes en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "etymology_texts": [
    "Dérivé du participe passé du verbe dream of (« rêver ») avec le préfixe négatif un-."
  ],
  "forms": [
    {
      "form": "more undreamed-of",
      "tags": [
        "comparative"
      ]
    },
    {
      "form": "most undreamed-of",
      "tags": [
        "superlative"
      ]
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "adj",
  "pos_title": "Adjectif",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Exemples en anglais",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Exemples en anglais à traduire",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "Mihaly Csikszentmihalyi, Flow, 1990",
          "text": "Why is it that, despite having achieved previously undreamed-of miracles of progress, we seem more helpless in facing life than our less privileged ancestors were?"
        }
      ],
      "glosses": [
        "Pas imaginé, pas expecté."
      ],
      "id": "fr-undreamed-of-en-adj-YeQeqQH1"
    }
  ],
  "word": "undreamed-of"
}

{
  "categories": [
    "Adjectifs en anglais",
    "Lemmes en anglais",
    "anglais"
  ],
  "etymology_texts": [
    "Dérivé du participe passé du verbe dream of (« rêver ») avec le préfixe négatif un-."
  ],
  "forms": [
    {
      "form": "more undreamed-of",
      "tags": [
        "comparative"
      ]
    },
    {
      "form": "most undreamed-of",
      "tags": [
        "superlative"
      ]
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "adj",
  "pos_title": "Adjectif",
  "senses": [
    {
      "categories": [
        "Exemples en anglais",
        "Exemples en anglais à traduire"
      ],
      "examples": [
        {
          "ref": "Mihaly Csikszentmihalyi, Flow, 1990",
          "text": "Why is it that, despite having achieved previously undreamed-of miracles of progress, we seem more helpless in facing life than our less privileged ancestors were?"
        }
      ],
      "glosses": [
        "Pas imaginé, pas expecté."
      ]
    }
  ],
  "word": "undreamed-of"
}