n. A commander-in-chief; a supreme leader of an army or of armies.n. The sovereign or supreme ruler of an empire: a title of dignity conventionally superior to that of king: as, the emperor of Germany or of Russia. See empire.n. In zoöl.: In entomology: One of several large sphinxes or moths: as, the peacock emperor, Saturnia pavonia. One of several large butterflies of the family Nymphalidæ: as, the purple emperor, the popular name in Great Britain of Apatura iris, also called the purple high-flier; the tawny emperor, A. herse. See Apatura.n. In ornithology, one of sundry birds notable of their kind.n. A large boa of Central America, Boa imperator, probably a variety of the Boa constrictor.n. Synonyms Monarch, etc. See prince.n. [capitalized] The trade-name of a standard quality of fine English drawing-paper made in sheets 72 by 48 inches.