also: わたばね
noun
down feather; plumule
Technical ornithological term for the soft, fluffy feathers found on young birds or under the outer feathers of adults.
ひな鳥は綿羽で覆われている。
The chick is covered with down feathers.
この図鑑には綿羽の拡大写真が載っている。
This field guide has a close-up photo of a down feather.
羽毛 is the general term for feathers or plumage, while 綿羽 specifically refers to down feathers.
Compound of 綿 (cotton, fluffy) and 羽 (feather). The reading めんう uses the on'yomi of both characters, while わたばね uses the kun'yomi of 綿 and the kun'yomi of 羽.