'scathingly' originates from the word 'scathe,' which comes from Old Norse 'skaði,' meaning 'harm' or 'injury.'

'scathe' transformed into the Middle English word 'scathen,' and eventually became the modern English word 'scathe,' with 'scathingly' as its adverbial form.

Initially, it meant 'to harm or injure,' but over time it evolved into its current meaning of 'severely critical.'