Pegasus

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. In class, myth., the winged horse of the Muses, sprung from the blood of Medusa when slain by perseus. With a stroke of his hoof he was fabled to have caused to well forth, on Mount Helicon in Bœotia, the poetically inspiring fountain Hippocrene. He was ultimately changed into a constellation.
2. n. One of the ancient northern constellations. The figure represents the forward half of a winged horse.The center of the constellation is about 20 degrees north of the equator, and four bright stars in it form a large square.
3. n. [NL.] In ichthyology, the typical genus of Pegasidæ, containing fishes of strange form, suggestive of the winged horse of classic mythology.

Wiktionary

1. n. 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.
2. n. 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.
3. n. 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.
4. n. historical A coin of ancient Corinth, with a winged horse depicted on the obverse.

GNU Webster's 1913

1. n. (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.
2. n. (Astron.) A northen constellation near the vernal equinoctial point. Its three brightest stars, with the brightest star of Andromeda, form the square of Pegasus.
3. n. (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.

WordNet 3.0

1. n. (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
2. n. a constellation in the northern hemisphere near Andromeda and Pisces