What does "emperor" mean?

Emperor: The sovereign or supreme monarch of an empire; -- a title of dignity superior to that of king; as, the emperor of Germany or of Austria; the emperor or Czar of Russia. Emperor goose (Zoöl.), a large and handsome goose (Philacte canagica), found in Alaska. -- Emperor moth (Zoöl.), one of several large and beautiful bombycid moths, with transparent spots on the wings; as the American Cecropia moth (Platysamia cecropia), and the European species (Saturnia pavonia). -- Emperor paper. See under Paper. -- Purple emperor (Zoöl.), a large, strong British butterfly (Apatura iris).