Third person singular or plural of appall; shocks or horrifies someone greatly.
From Old French 'apalir' (to grow pale), derived from Latin 'ad-' (to) and 'pallere' (to be pale), originally describing the physical reaction of shock or horror.
The original meaning was literally to 'make pale'—when you're appalled, your face actually does go pale, which is why this word started with the physical reaction.
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