Achelous (ăkˌəlōˈəs) [key], in Greek mythology, river god; son of Oceanus and Tethys. He possessed the power to appear as a bull, a serpent, or a bullheaded man. Hercules defeated him and broke off one of his horns, which, according to one legend, became the cornucopia. He is sometimes said to be the father of the Sirens.
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