"letra superior" meaning in Spanish

{
  "forms": [
    {
      "form": "letras superiores",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "f"
      },
      "expansion": "letra superior f (plural letras superiores)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "es",
          "name": "Letter names",
          "orig": "es:Letter names",
          "parents": [
            "Letters, symbols, and punctuation",
            "Names",
            "Orthography",
            "All topics",
            "Proper nouns",
            "Terms by semantic function",
            "Writing",
            "Fundamental",
            "Nouns",
            "Human behaviour",
            "Language",
            "Lemmas",
            "Human",
            "Communication"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Synonym of letra volada"
      ],
      "id": "en-letra_superior-es-noun-1bRB1KOy",
      "links": [
        [
          "letra volada",
          "letra volada#Spanish"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "letra volada"
        }
      ],
      "tags": [
        "feminine"
      ]
    }
  ],
  "word": "letra superior"
}

{
  "forms": [
    {
      "form": "letras superiores",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "f"
      },
      "expansion": "letra superior f (plural letras superiores)",
      "name": "es-noun"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Spanish countable nouns",
        "Spanish entries with incorrect language header",
        "Spanish feminine nouns",
        "Spanish lemmas",
        "Spanish multiword terms",
        "Spanish nouns",
        "es:Letter names"
      ],
      "glosses": [
        "Synonym of letra volada"
      ],
      "links": [
        [
          "letra volada",
          "letra volada#Spanish"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "letra volada"
        }
      ],
      "tags": [
        "feminine"
      ]
    }
  ],
  "word": "letra superior"
}