"εφιαλτικούς" meaning in Greek

{
  "forms": [
    {
      "form": "efialtikoús",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "el",
        "2": "adjf"
      },
      "expansion": "εφιαλτικούς • (efialtikoús)",
      "name": "head"
    }
  ],
  "lang": "Greek",
  "lang_code": "el",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Greek entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "form_of": [
        {
          "extra": "efialtikós",
          "word": "εφιαλτικός"
        }
      ],
      "glosses": [
        "accusative masculine plural of εφιαλτικός (efialtikós)"
      ],
      "id": "en-εφιαλτικούς-el-adj-JH6~Mus5",
      "links": [
        [
          "εφιαλτικός",
          "εφιαλτικός#Greek"
        ]
      ],
      "tags": [
        "accusative",
        "form-of",
        "masculine",
        "plural"
      ]
    }
  ],
  "word": "εφιαλτικούς"
}

{
  "forms": [
    {
      "form": "efialtikoús",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "el",
        "2": "adjf"
      },
      "expansion": "εφιαλτικούς • (efialtikoús)",
      "name": "head"
    }
  ],
  "lang": "Greek",
  "lang_code": "el",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "Greek adjective forms",
        "Greek entries with incorrect language header",
        "Greek non-lemma forms",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "form_of": [
        {
          "extra": "efialtikós",
          "word": "εφιαλτικός"
        }
      ],
      "glosses": [
        "accusative masculine plural of εφιαλτικός (efialtikós)"
      ],
      "links": [
        [
          "εφιαλτικός",
          "εφιαλτικός#Greek"
        ]
      ],
      "tags": [
        "accusative",
        "form-of",
        "masculine",
        "plural"
      ]
    }
  ],
  "word": "εφιαλτικούς"
}