"second in command" meaning in English

{
  "forms": [
    {
      "form": "seconds in command",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "seconds in command"
      },
      "expansion": "second in command (plural seconds in command)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "second-in-command"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2012 April 26, Tasha Robinson, “Film: Reviews: The Pirates! Band Of Misfits :”, in The Onion AV Club",
          "text": "None of it amounts to much, particularly given that it’s all in the service of a man wanting to win a meaningless contest he doesn’t deserve to win, and the question of whether his noodlehead crew and his surprisingly competent second in command (Martin Freeman) will still respect him throughout.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Alternative spelling of second-in-command"
      ],
      "id": "en-second_in_command-en-noun-fImMshMH",
      "links": [
        [
          "second-in-command",
          "second-in-command#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "second in command"
}

{
  "forms": [
    {
      "form": "seconds in command",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "seconds in command"
      },
      "expansion": "second in command (plural seconds in command)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "second-in-command"
        }
      ],
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations"
      ],
      "examples": [
        {
          "ref": "2012 April 26, Tasha Robinson, “Film: Reviews: The Pirates! Band Of Misfits :”, in The Onion AV Club",
          "text": "None of it amounts to much, particularly given that it’s all in the service of a man wanting to win a meaningless contest he doesn’t deserve to win, and the question of whether his noodlehead crew and his surprisingly competent second in command (Martin Freeman) will still respect him throughout.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Alternative spelling of second-in-command"
      ],
      "links": [
        [
          "second-in-command",
          "second-in-command#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    }
  ],
  "word": "second in command"
}