verb (appals, appalling, appalled)[with object] (usually be appalled)
Middle English: from Old French apalir 'grow pale', from a- (from Latin ad 'to, at') + palir 'to pale'. The original sense was 'grow pale', later 'make pale', hence 'horrify' (late Middle English)
Spell appal with a double p.
Double the l when adding endings which begin with a vowel to words which end in a vowel plus l (as in travel): (appals, appalling, appalled).