"drost" meaning in Welsh

{
  "etymology_text": "From drost-, the stem of inflected personal forms of dros.",
  "head_templates": [
    {
      "args": {
        "1": "cy",
        "2": "preposition",
        "3": "triggers soft mutation"
      },
      "expansion": "drost (triggers soft mutation)",
      "name": "head"
    }
  ],
  "lang": "Welsh",
  "lang_code": "cy",
  "pos": "prep",
  "senses": [
    {
      "alt_of": [
        {
          "word": "dros"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Welsh entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Welsh prepositions",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Alternative form of dros"
      ],
      "id": "en-drost-cy-prep-6MFq7qgS",
      "links": [
        [
          "dros",
          "dros#Welsh"
        ]
      ],
      "raw_glosses": [
        "(North Wales, colloquial) Alternative form of dros"
      ],
      "tags": [
        "North-Wales",
        "alt-of",
        "alternative",
        "colloquial"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/drɔsd/"
    },
    {
      "ipa": "[drɔst]"
    }
  ],
  "word": "drost"
}

{
  "etymology_text": "From drost-, the stem of inflected personal forms of dros.",
  "head_templates": [
    {
      "args": {
        "1": "cy",
        "2": "preposition",
        "3": "triggers soft mutation"
      },
      "expansion": "drost (triggers soft mutation)",
      "name": "head"
    }
  ],
  "lang": "Welsh",
  "lang_code": "cy",
  "pos": "prep",
  "senses": [
    {
      "alt_of": [
        {
          "word": "dros"
        }
      ],
      "categories": [
        "Welsh entries with incorrect language header",
        "Welsh lemmas",
        "Welsh prepositions",
        "Welsh terms with IPA pronunciation"
      ],
      "glosses": [
        "Alternative form of dros"
      ],
      "links": [
        [
          "dros",
          "dros#Welsh"
        ]
      ],
      "raw_glosses": [
        "(North Wales, colloquial) Alternative form of dros"
      ],
      "tags": [
        "North-Wales",
        "alt-of",
        "alternative",
        "colloquial"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/drɔsd/"
    },
    {
      "ipa": "[drɔst]"
    }
  ],
  "word": "drost"
}

{
  "called_from": "form_descriptions/1698",
  "msg": "unrecognized head form: triggers soft mutation",
  "path": [
    "drost"
  ],
  "section": "Welsh",
  "subsection": "preposition",
  "title": "drost",
  "trace": ""
}