"aC" meaning in Spanish

{
  "etymology_templates": [
    {
      "args": {
        "1": "es",
        "2": "antes de Cristo"
      },
      "expansion": "Abbreviation of antes de Cristo",
      "name": "abbrev"
    }
  ],
  "etymology_text": "Abbreviation of antes de Cristo.",
  "head_templates": [
    {
      "args": {},
      "expansion": "aC",
      "name": "es-adv"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Pages with 3 entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "english": "The city of Hippos was founded in the second century BC and came to hold seven churches.",
          "ref": "2019 September 4, “Un mosaico podría aportar nuevos datos sobre el milagro de Jesús de la multiplicación de los panes”, in Clarín:",
          "text": "La ciudad de Hipos se fundó en el siglo II aC y llegó a albergar siete iglesias.",
          "type": "quote"
        }
      ],
      "glosses": [
        "BC (Before Christ)"
      ],
      "id": "en-aC-es-adv-PXwpeJKA",
      "links": [
        [
          "BC",
          "BC"
        ]
      ]
    }
  ],
  "word": "aC"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "es",
        "2": "antes de Cristo"
      },
      "expansion": "Abbreviation of antes de Cristo",
      "name": "abbrev"
    }
  ],
  "etymology_text": "Abbreviation of antes de Cristo.",
  "head_templates": [
    {
      "args": {},
      "expansion": "aC",
      "name": "es-adv"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "adv",
  "senses": [
    {
      "categories": [
        "Pages with 3 entries",
        "Pages with entries",
        "Spanish abbreviations",
        "Spanish adverbs",
        "Spanish entries with incorrect language header",
        "Spanish lemmas",
        "Spanish terms with quotations"
      ],
      "examples": [
        {
          "english": "The city of Hippos was founded in the second century BC and came to hold seven churches.",
          "ref": "2019 September 4, “Un mosaico podría aportar nuevos datos sobre el milagro de Jesús de la multiplicación de los panes”, in Clarín:",
          "text": "La ciudad de Hipos se fundó en el siglo II aC y llegó a albergar siete iglesias.",
          "type": "quote"
        }
      ],
      "glosses": [
        "BC (Before Christ)"
      ],
      "links": [
        [
          "BC",
          "BC"
        ]
      ]
    }
  ],
  "word": "aC"
}