a large white bird with a long neck that lives on rivers and lakes.——朗文当代大辞典

A large web-footed swimming bird of the genus Cygnus or subfamily Cygninæ of the family Anatidæ, characterized by a long and gracefully curved neck and a majestic motion when swimming; esp. C. olor, C. gibbus, or C. mansuetus, with pure white plumage in the adult, black legs and feet, and a red bill surmounted by a black knob, named specifically the Domestic, Mute, or Tame Swan.——牛津当代大辞典  @en