"C." meaning in Latin

{
  "etymology_text": "From archaic Latin, when the letter C represented the phonetic value /g/.",
  "head_templates": [
    {
      "args": {
        "1": "C.",
        "g": "m",
        "indecl": "1"
      },
      "expansion": "C. m (indeclinable)",
      "name": "la-proper noun"
    }
  ],
  "lang": "Latin",
  "lang_code": "la",
  "pos": "name",
  "senses": [
    {
      "alt_of": [
        {
          "word": "Cāius and Gāius"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Latin entries with incorrect language header",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 4 entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Praenominal abbreviation of Cāius and Gāius."
      ],
      "id": "en-C.-la-name-njpf9wB0",
      "links": [
        [
          "Praenominal",
          "praenomen#English"
        ],
        [
          "Cāius",
          "Caius#Latin"
        ],
        [
          "Gāius",
          "Gaius#Latin"
        ]
      ],
      "tags": [
        "Praenominal",
        "abbreviation",
        "alt-of",
        "indeclinable",
        "masculine"
      ]
    }
  ],
  "word": "C."
}

{
  "etymology_text": "From archaic Latin, when the letter C represented the phonetic value /g/.",
  "head_templates": [
    {
      "args": {
        "1": "C.",
        "g": "m",
        "indecl": "1"
      },
      "expansion": "C. m (indeclinable)",
      "name": "la-proper noun"
    }
  ],
  "lang": "Latin",
  "lang_code": "la",
  "pos": "name",
  "senses": [
    {
      "alt_of": [
        {
          "word": "Cāius and Gāius"
        }
      ],
      "categories": [
        "Latin abbreviations",
        "Latin entries with incorrect language header",
        "Latin indeclinable nouns",
        "Latin lemmas",
        "Latin masculine indeclinable nouns",
        "Latin masculine nouns",
        "Latin praenominal abbreviations",
        "Latin proper nouns",
        "Latin terms spelled with .",
        "Pages with 4 entries",
        "Pages with entries"
      ],
      "glosses": [
        "Praenominal abbreviation of Cāius and Gāius."
      ],
      "links": [
        [
          "Praenominal",
          "praenomen#English"
        ],
        [
          "Cāius",
          "Caius#Latin"
        ],
        [
          "Gāius",
          "Gaius#Latin"
        ]
      ],
      "tags": [
        "Praenominal",
        "abbreviation",
        "alt-of",
        "indeclinable",
        "masculine"
      ]
    }
  ],
  "word": "C."
}