any one of numerous species of large aquatic birds belonging to cygnus, olor, and allied genera of the subfamily cygninae. they have a large and strong beak and a long neck, and are noted for their graceful movements when swimming. most of the northern species are white. in literature the swan was fabled to sing a melodious song, especially at the time of its death.-fig.: an appellation for a sweet singer, or a poet noted for grace and melody; as shakespeare is called the swan of avon.-the constellation cygnus.