Refers to the feathers of birds collectively, including both contour feathers and soft down. Often used in contexts like bedding, clothing, and bird description.
This futon uses a lot of down.
The bird's plumage is very beautiful.
This cushion is made of down.
The bird's feathers had fallen out and were lying on the floor.
The craftsman gathered down to make the futon.
羽毛 is the more specific, often formal term for down or feathers (as in bedding), while 毛 can loosely describe a bird's soft covering too.
羽毛 is the standard, concrete word for feathers or down, whereas 羽衣 is a figurative, literary expression for plumage.
羽毛 (feathers/down from birds) and 羊毛 (wool from sheep) look similar since both end in 毛, but they come from completely different animals and materials.
Composed of 羽 (う, 'feather') and 毛 (もう, 'hair/fur'). The reading うもう is the standard on'yomi compound reading.