Pegasus, the winged horse, begotten of Poseidon, who sprung from the body of Medusa when Perseus swooped off her head, and who with a stroke of his hoof broke open the spring of Hippocrene on Mount Helicon, and mounted on whom Bellerophon slew the Chimera, and by means of which he hoped, if he had not been thrown, to ascend to heaven, as Pegasus did alone, becoming thereafter a constellation in the sky; this is the winged horse upon whose back poets, to the like disappointment, hope to scale the empyrean, who have not, like Bellerophon, first distinguished themselves by slaying Chimeras.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Peers, The Twelve * Pegu