"mega-annum" meaning in English

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "mega",
        "3": "annum"
      },
      "expansion": "mega- + annum",
      "name": "prefix"
    }
  ],
  "etymology_text": "From mega- + annum.",
  "forms": [
    {
      "form": "mega-annums",
      "tags": [
        "plural"
      ]
    },
    {
      "form": "mega-anna",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "s",
        "2": "mega-anna"
      },
      "expansion": "mega-annum (plural mega-annums or mega-anna)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
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          "source": "w"
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          "parents": [
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          "source": "w"
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          "kind": "other",
          "name": "English hybridisms",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms prefixed with mega-",
          "parents": [],
          "source": "w"
        },
        {
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          "parents": [
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      ],
      "glosses": [
        "Synonym of megayear: a period of 1 million years."
      ],
      "id": "en-mega-annum-en-noun-PPdfTjH-",
      "links": [
        [
          "megayear",
          "megayear#English"
        ],
        [
          "period",
          "period"
        ],
        [
          "million",
          "million"
        ],
        [
          "year",
          "year"
        ]
      ],
      "related": [
        {
          "word": "gigannum"
        }
      ],
      "synonyms": [
        {
          "extra": "a period of 1 million years",
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "megayear"
        },
        {
          "word": "megannum"
        },
        {
          "word": "megaannum"
        },
        {
          "word": "mega annum"
        },
        {
          "word": "Mega annum"
        },
        {
          "tags": [
            "abbreviation"
          ],
          "word": "Ma"
        }
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ˌmɛɡəˈænəm/"
    }
  ],
  "word": "mega-annum"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "mega",
        "3": "annum"
      },
      "expansion": "mega- + annum",
      "name": "prefix"
    }
  ],
  "etymology_text": "From mega- + annum.",
  "forms": [
    {
      "form": "mega-annums",
      "tags": [
        "plural"
      ]
    },
    {
      "form": "mega-anna",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "s",
        "2": "mega-anna"
      },
      "expansion": "mega-annum (plural mega-annums or mega-anna)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "gigannum"
    }
  ],
  "senses": [
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        "English terms prefixed with mega-",
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      ],
      "glosses": [
        "Synonym of megayear: a period of 1 million years."
      ],
      "links": [
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          "megayear",
          "megayear#English"
        ],
        [
          "period",
          "period"
        ],
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          "million",
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        ],
        [
          "year",
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      ],
      "synonyms": [
        {
          "extra": "a period of 1 million years",
          "tags": [
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          "word": "megayear"
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      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ˌmɛɡəˈænəm/"
    }
  ],
  "synonyms": [
    {
      "word": "megannum"
    },
    {
      "word": "megaannum"
    },
    {
      "word": "mega annum"
    },
    {
      "word": "Mega annum"
    },
    {
      "tags": [
        "abbreviation"
      ],
      "word": "Ma"
    }
  ],
  "word": "mega-annum"
}