"by the sly" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "by the sly (not comparable)",
      "name": "en-adv"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1859, George Eliot, The Lifted Veil",
          "text": "I read Plutarch, and Shakespeare, and Don Quixote by the sly, and supplied myself in that way with wandering thoughts, while my tutor was assuring me that \"an improved man, as distinguished from an ignorant one, was a man who knew the reason why water ran downhill.\"",
          "type": "quotation"
        }
      ],
      "glosses": [
        "on the sly"
      ],
      "id": "en-by_the_sly-en-adv-nP2FkD3c",
      "links": [
        [
          "on the sly",
          "on the sly"
        ]
      ],
      "raw_glosses": [
        "(dated) on the sly"
      ],
      "tags": [
        "dated",
        "not-comparable"
      ]
    }
  ],
  "word": "by the sly"
}

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "by the sly (not comparable)",
      "name": "en-adv"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        "English adverbs",
        "English dated terms",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English terms with quotations",
        "English uncomparable adverbs",
        "Quotation templates to be cleaned"
      ],
      "examples": [
        {
          "ref": "1859, George Eliot, The Lifted Veil",
          "text": "I read Plutarch, and Shakespeare, and Don Quixote by the sly, and supplied myself in that way with wandering thoughts, while my tutor was assuring me that \"an improved man, as distinguished from an ignorant one, was a man who knew the reason why water ran downhill.\"",
          "type": "quotation"
        }
      ],
      "glosses": [
        "on the sly"
      ],
      "links": [
        [
          "on the sly",
          "on the sly"
        ]
      ],
      "raw_glosses": [
        "(dated) on the sly"
      ],
      "tags": [
        "dated",
        "not-comparable"
      ]
    }
  ],
  "word": "by the sly"
}