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

'appal' changed from Old French word 'apalir' and Middle English 'appallen' and eventually became the modern English word 'appal' (also spelled 'appall').

Initially, it meant 'to make pale (with fear or shock)', but over time it evolved into its current meaning of 'to horrify or greatly dismay'.