"submillisievert" meaning in English

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "sub",
        "3": "millisievert"
      },
      "expansion": "sub- + millisievert",
      "name": "prefix"
    }
  ],
  "etymology_text": "sub- + millisievert",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "submillisievert (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms prefixed with sub-",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Less than a millisievert"
      ],
      "id": "en-submillisievert-en-adj-UBuqL1HQ",
      "links": [
        [
          "millisievert",
          "millisievert"
        ]
      ],
      "raw_glosses": [
        "(of a radiation dose) Less than a millisievert"
      ],
      "raw_tags": [
        "of a radiation dose"
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "submillisievert"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "sub",
        "3": "millisievert"
      },
      "expansion": "sub- + millisievert",
      "name": "prefix"
    }
  ],
  "etymology_text": "sub- + millisievert",
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "submillisievert (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "English adjectives",
        "English entries with incorrect language header",
        "English lemmas",
        "English terms prefixed with sub-",
        "English uncomparable adjectives"
      ],
      "glosses": [
        "Less than a millisievert"
      ],
      "links": [
        [
          "millisievert",
          "millisievert"
        ]
      ],
      "raw_glosses": [
        "(of a radiation dose) Less than a millisievert"
      ],
      "raw_tags": [
        "of a radiation dose"
      ],
      "tags": [
        "not-comparable"
      ]
    }
  ],
  "word": "submillisievert"
}