The word "dress" can generically encompass all types of dresses from sun dresses to cocktail dresses. A gown is more of a formal "dress" and is worn for very special occasions and is typically quite fancy.

Dress is a simple wardrobe item. Gown can be an "evening", in this meaning it is a dress, maybe for celebrations, and can be a "morning", this is the item, that we use after bath

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