- The butterfly genus Cycnus is now synonymized with Panthiades.
In Greek mythology, multiple characters were known as Cycnus (Ancient Greek: Κύκνος) or Cygnus. The literal meaning of the name is "swan", and accordingly most of them ended up being transformed into swans.
- Cycnus, one of the suitors of Penelope.
- Cycnus, son of King Eredion of Achaea, who, in one version, seduced Leda and made her mother of triplets: the Dioscuri and Helen. In all other sources, she had these children by Zeus who approached her in the shape of a swan (kyknos).
- Cycnus, a blunder for Guneus in the manuscript of Hyginus' Fab. 97 (list of the Achaean leaders against Troy).
According to Pseudo-Eratosthenes and Hyginus' Poetical Astronomy, the constellation Cygnus was the stellar image of the swan Zeus had transformed into in order to seduce Leda or Nemesis.