'additionally' originates from the Latin word 'additio', where 'ad-' meant 'toward' and 'ditio' meant 'giving'.

'additio' transformed into the Old French word 'addition', and eventually became the modern English word 'additional', with 'additionally' as its adverbial form.

Initially, it meant 'to give or add something', but over time it evolved into its current meaning of 'in addition'.