羽毛

1. Origins, structure, and basic meaning

• Structure: 羽毛 is read as うもう and is a noun for a feather or for light down used as filling.
• Basic usage: An individual appears as 羽毛が一枚, while filling is described with 羽毛が詰められている.

2. Common pitfalls and similar expressions

• One feather and collective down
  • The item on the water is a single feather, whereas the coat contains down treated collectively as material.
• Counter in context
  • 一枚 counts the flat individual feather; it does not count the coat's filling as one unit.