In Greek mythology, Theonoe (Ancient Greek: Θεονόη, romanized: Theonóē, lit. 'she of god-like mind') is a character in Athenian playwright Euripides' play Helen. She is presented as the daughter of the Egyptian king, Proteus, and the Nereid Psamathe. She was the sister of Theoclymenus, the current king of Egypt. Her name means "divine wisdom," coming from theós 'god' and nóos or noûs 'mind.' Theonoe's earlier name was Eido (Eidothea).