noun
winter fur; winter coat; winter plumage
Refers to the thick fur or feathers that animals grow for winter. Used for mammals and birds.
ウサギは冬になると冬毛に生え変わる。
Rabbits grow their winter coat when winter comes.
この鳥の冬毛は夏よりも白っぽい。
This bird's winter plumage is whiter than in summer.