noun
circular window; round window
A window that is circular in shape, often found in traditional Japanese architecture, ships, or modern design.
茶室の丸窓から庭が見える。
The garden can be seen through the circular window of the tea room.
船の丸窓から海を眺めた。
I looked out at the sea through the ship's round window.
Compound of 丸 (maru, 'round') + 窓 (mado, 'window'). The alternate spelling 円窓 uses 円 (en/maru, 'circle') for the same meaning.