(of Botia). A fisherman who instructed Apollo in soothsaying. He jumped into the sea, and became a marine god. Milton alludes to him in his Comus (line 895):
“[By] old soothsaying Glaucus' spell.”
(Another). In Latin, Glaucus alter. One who ruins himself by horses. The tale is that Glaucus, son of Sisyphus, would not allow his horses to breed, and the goddess of Love so infuriated them that they killed him.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894