'anti-paedo-baptism' is formed from the prefix 'anti-' (from Greek 'anti' meaning 'against'), the combining form 'paedo-' (from Greek 'pais/paidos' meaning 'child'), and 'baptism' (from Greek 'baptisma'/'baptizein' meaning 'to dip or immerse').

'baptism' entered English via Latin 'baptisma' and Old French 'baptisme'; the combining form 'paedo-' (also seen in spellings like 'paedo-'/'pedo-') was used to form 'paedobaptism' meaning infant baptism; later, English speakers attached the prefix 'anti-' to indicate opposition, producing 'anti-paedo-baptism'.

Originally 'baptism' referred to the physical act of dipping or immersion; over time it came to denote the Christian sacrament. 'Paedobaptism' specifically came to mean baptism of infants, and 'anti-paedo-baptism' developed to denote opposition to that practice, typically favoring believer's baptism.