A heavy coat worn over clothes in winter WordNet 3.0 & Open English WordNet

A greatcoat is a large, woollen overcoat designed for warmth and protection against wind and weather, and features a collar that can be turned up and cuffs that can be turned down to protect the face and the hands, whilst the short rain-cape at the shoulders protects from the wind and repels rain. Wikipedia

Oversized, heavy overcoat Wikidata

A heavy garment worn over other clothes, for protection from cold or weather. Wiktionary

Garment. Wiktionary (translation)