"occult line" meaning in English

{
  "forms": [
    {
      "form": "occult lines",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "occult line (plural occult lines)",
      "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"
          ],
          "source": "w"
        },
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          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1854, William Henry Smyth, The Mediterranean: A Memoir Physical, Historical, and Nautical, pages 136–37:",
          "text": "Yet in making an occult line on my chart, to indicate this rise from a depth at present beyond estimate, I by no means meant it as a mark for shoal water in which navigation is concerned.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A line drawn as a part of the construction of a geometrical figure or problem, but not to appear in the finished plan."
      ],
      "id": "en-occult_line-en-noun-LLflPhf5",
      "links": [
        [
          "construction",
          "construction"
        ],
        [
          "geometrical",
          "geometrical"
        ],
        [
          "figure",
          "figure"
        ],
        [
          "problem",
          "problem"
        ]
      ]
    }
  ],
  "word": "occult line"
}

{
  "forms": [
    {
      "form": "occult lines",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "occult line (plural occult lines)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "Pages with 1 entry",
        "Pages with entries",
        "Quotation templates to be cleaned"
      ],
      "examples": [
        {
          "ref": "1854, William Henry Smyth, The Mediterranean: A Memoir Physical, Historical, and Nautical, pages 136–37:",
          "text": "Yet in making an occult line on my chart, to indicate this rise from a depth at present beyond estimate, I by no means meant it as a mark for shoal water in which navigation is concerned.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A line drawn as a part of the construction of a geometrical figure or problem, but not to appear in the finished plan."
      ],
      "links": [
        [
          "construction",
          "construction"
        ],
        [
          "geometrical",
          "geometrical"
        ],
        [
          "figure",
          "figure"
        ],
        [
          "problem",
          "problem"
        ]
      ]
    }
  ],
  "word": "occult line"
}