Pegasus

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Greek Mythology A winged horse that with a stroke of his hoof caused the fountain Hippocrene to spring forth from Mount Helicon.
• noun A constellation in the Northern Hemisphere near Aquarius and Andromeda.

from The Century Dictionary.

• noun In class, myth., the winged horse of the Muses, sprung from the blood of Medusa when slain by perseus.
• noun One of the ancient northern constellations.
• noun [NL.] In ichthyology, the typical genus of Pegasidæ, containing fishes of strange form, suggestive of the winged horse of classic mythology.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Gr. Myth.) A winged horse fabled to have sprung from the body of Medusa when she was slain. He is noted for causing, with a blow of his hoof, Hippocrene, the inspiring fountain of the Muses, to spring from Mount Helicon. On this account he is, in modern times, associated with the Muses, and with ideas of poetic inspiration.
• noun (Astron.) A northen constellation near the vernal equinoctial point. Its three brightest stars, with the brightest star of Andromeda, form the square of Pegasus.
• noun (Zoöl.) A genus of small fishes, having large pectoral fins, and the body covered with hard, bony plates. Several species are known from the East Indies and China.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun A taxonomic genus within the family Pegasidae — small fish with pectoral fins and body covered with hard, bony plates, from the East Indies and China.
• proper noun Greek mythology A winged horse fabled to have sprung from the neck of Medusa when she was slain. He is noted for causing, with a blow of his hoof, Hippocrene, the inspiring fountain of the Muses, to spring from Mount Helicon. Bellerophon rode Pegasus when he defeated the Chimaera.
• proper noun astronomy An autumn constellation of the northern sky, near the vernal equinoctial point, said to resemble the mythical horse. Its three brightest stars, with the brightest star of Andromeda, form the square of Pegasus. It contains the stars Markab and Algenib.
• noun historical A coin of ancient Corinth, with a winged horse depicted on the obverse.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (Greek mythology) the immortal winged horse that sprang from the blood of the slain Medusa; was tamed by Bellerophon with the help of a bridle given him by Athena; as the flying horse of the Muses it is a symbol of highflying imagination
• noun a constellation in the northern hemisphere near Andromeda and Pisces