noun
merganser
Refers to any duck of the genus Mergus, a diving duck with a slender serrated bill. In everyday contexts, the katakana form アイサ is most common.
アイサは魚を捕るのが上手な水鳥です。
The merganser is a waterbird skilled at catching fish.
冬になると、この湖にアイサが飛来します。
In winter, mergansers come to this lake.
The Japanese name アイサ (aisa) is of uncertain origin. It may be derived from the bird's call or from an older Japanese word, but the exact derivation is unclear.