'adulterously' originates from Latin, specifically the word 'adulterare,' where 'ad-' meant 'to' and 'alter' meant 'other.'

'adulterare' transformed into the Old French word 'adulterer,' and eventually became the modern English word 'adulterous' through Middle English.

Initially, it meant 'to corrupt or make impure,' but over time it evolved into its current meaning of 'engaging in adultery.'