In Old English, éo represents a diphthong, a single vowel sound combining ay with a short o as in 'dot' or 'cloth'. So éo is pronounced somewhat like 'ayo', but as a single sound.

Théoden's name comes from a real Anglo-Saxon word that originally meant 'leader of the people'. The element théod, 'people', occurs in many of the names of the Rohirrim, and also in their ancestral name, Éothéod, meaning 'Horse People'.