'appall' originates from Old French, specifically the word 'apalir,' where 'a-' meant 'to' and 'palir' meant 'to grow pale.'

'apalir' transformed into the Middle English word 'appallen,' and eventually became the modern English word 'appall.'

Initially, it meant 'to grow pale,' but over time it evolved into its current meaning of 'to fill with horror or dismay.'