'mystagogue' originates from Greek, specifically the word 'mystagōgos', where 'mustēs' (myst-) meant 'one initiated into the mysteries' and 'agōgos' meant 'leader' or 'guide'.

'mystagōgos' passed into Late Latin and Medieval Latin as 'mystagogus' and then into English (via Middle English forms) as the modern English word 'mystagogue'.

Initially, it meant 'leader of initiates in religious mysteries'; over time it has retained that core meaning but has broadened to include anyone who guides or explains obscure/esoteric doctrines.