"ἐθνάρχου" meaning in Ancient Greek

{
  "forms": [
    {
      "form": "ethnárkhou",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "grc",
        "2": "noun form"
      },
      "expansion": "ἐθνάρχου • (ethnárkhou)",
      "name": "head"
    }
  ],
  "lang": "Ancient Greek",
  "lang_code": "grc",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Ancient Greek entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "form_of": [
        {
          "extra": "ethnárkhēs",
          "word": "ἐθνάρχης"
        }
      ],
      "glosses": [
        "genitive singular of ἐθνάρχης (ethnárkhēs)"
      ],
      "id": "en-ἐθνάρχου-grc-noun-lcc-Gsac",
      "links": [
        [
          "ἐθνάρχης",
          "ἐθνάρχης#Ancient Greek"
        ]
      ],
      "related": [
        {
          "roman": "Ethnárchou",
          "word": "Εθνάρχου"
        },
        {
          "roman": "ethnárchi",
          "word": "εθνάρχη"
        }
      ],
      "tags": [
        "form-of",
        "genitive",
        "singular"
      ]
    }
  ],
  "word": "ἐθνάρχου"
}

{
  "forms": [
    {
      "form": "ethnárkhou",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "grc",
        "2": "noun form"
      },
      "expansion": "ἐθνάρχου • (ethnárkhou)",
      "name": "head"
    }
  ],
  "lang": "Ancient Greek",
  "lang_code": "grc",
  "pos": "noun",
  "related": [
    {
      "roman": "Ethnárchou",
      "word": "Εθνάρχου"
    },
    {
      "roman": "ethnárchi",
      "word": "εθνάρχη"
    }
  ],
  "senses": [
    {
      "categories": [
        "Ancient Greek entries with incorrect language header",
        "Ancient Greek non-lemma forms",
        "Ancient Greek noun forms"
      ],
      "form_of": [
        {
          "extra": "ethnárkhēs",
          "word": "ἐθνάρχης"
        }
      ],
      "glosses": [
        "genitive singular of ἐθνάρχης (ethnárkhēs)"
      ],
      "links": [
        [
          "ἐθνάρχης",
          "ἐθνάρχης#Ancient Greek"
        ]
      ],
      "tags": [
        "form-of",
        "genitive",
        "singular"
      ]
    }
  ],
  "word": "ἐθνάρχου"
}