The Collaborative International Dictionary of English v.0.48:

Emperor \Em"per*or\, n. [OF. empereor, empereour, F. empereur,
   L. imperator, fr. imperare to command; in in + parare to
   prepare, order. See Parade, and cf. Imperative,
   Empress.]
   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.
   [1913 Webster]

   Emperor goose (Zo["o]l.), a large and handsome goose
      (Philacte canagica), found in Alaska.

   Emperor moth (Zo["o]l.), 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 (Zo["o]l.), a large, strong British
      butterfly (Apatura iris).
      [1913 Webster]

WordNet (r) 3.0 (2006):

Saturnia pavonia
    n 1: large moth of temperate forests of Eurasia having heavily
         scaled transparent wings [syn: emperor, emperor moth,
         Saturnia pavonia]