Horrified by phone game called "Decapitation" (8)

I believe the answer is:

appalled

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'horrified' is the definition.
('appal' can be a synonym of 'horrify')

I don't understand how the rest of the clue works.

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(Other definitions for appalled that I've seen before include "Aghast, horrified" , "Dismayed - aghast" , "Scandalised" , "Shocked and horrified" , "Deeply shocked, filled with dismay" .)

I've seen this clue in the Sydney Morning Herald.

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