Definition of Pegasus
1 Greek Mythology a winged horse that sprang from the blood of Medusa when Perseus cut off her head. 2 Astronomy a large northern constellation, said to represent a winged horse. The three brightest stars, together with one star of Andromeda, form the prominent Square of Pegasus.
(as genitive Pegasi
/ˈpegəsī/) used with a preceding letter or numeral to designate a star in this constellation:the star Zeta Pegasi