'remorselessly' originates from the English word 'remorseless,' which is derived from the Latin word 'remorsus,' where 're-' meant 'again' and 'mordere' meant 'to bite.'

'remorsus' transformed into the Middle English word 'remorse,' and eventually became the modern English word 'remorseless' with the addition of the suffix '-less' to indicate the absence of remorse.

Initially, it meant 'without biting back,' but over time it evolved into its current meaning of 'without pity or compassion.'