ˈswänzˌdau̇n also -wȯn- noun
Etymology: swan's (gen. of swan ) (I) + down
1. : the soft downy feathers of the swan especially when used as trimming on articles of dress
she was wrapped in grey satin edged with swansdown — Victoria Sackville-West
2. : a heavy cotton flannel with a thick nap on the face made with sateen weave