From Egyptian

Greek form of Egyptian ?st (reconstructed as Iset, Aset or Ueset), possibly from st meaning "throne". In Egyptian mythology Isis was the goddess of the sky and nature, the wife of Osiris and the mother of Horus. She was originally depicted wearing a throne-shaped headdress, but in later times she was conflated with the goddess Hathor and depicted having the horns of a cow on her head. She was also worshipped by people outside of Egypt, such as the Greeks and Romans.