'baptismally' originates from Late Latin, specifically the word 'baptismalis', where the element 'baptisma' (from Greek 'baptisma') meant 'a dipping' or 'immersion'.

'baptismally' developed from the adjective 'baptismal' in English; 'baptismal' came into Middle English from Old French and from Latin 'baptismalis', ultimately from Greek 'baptizein'/'baptisma'. The adverbial form was created by adding the English adverbial suffix '-ly' to 'baptismal'.

Initially the root referred specifically to the act of dipping or immersion; over time it came to denote matters 'pertaining to baptism', and the adverbial form now means 'in a baptismal manner' or 'by means of baptism'.