'autodidact' originates from Modern French 'autodidacte', ultimately from Greek 'autodidaktos', where 'auto-' meant 'self' and 'didaktos' meant 'taught'.

'autodidaktos' (Greek) passed into Modern French as 'autodidacte' and was adopted into English in the 19th century as 'autodidact'.

Initially it meant 'self-taught' (literally 'self-taught one'), and over time it has retained that meaning in modern usage.