UK:*UK and possibly other pronunciationsUK and possibly other pronunciations/əˈgɑːst/US:USA pronunciation: IPA and respellingUSA pronuncation: IPA/əˈgæst/ ,USA pronunciation: respelling(ə gast, ə gäst)

WordReference Random House Learner's Dictionary of American English © 2020
a•ghast /əˈgæst/USA pronunciation   adj. 
  1. [be + ~] filled with sudden fear, horror, or amazement:was aghast after witnessing the accident.

WordReference Random House Unabridged Dictionary of American English © 2020
a•ghast  (ə gast, ə gäst),USA pronunciation adj. 
  1. struck with overwhelming shock or amazement;
    filled with sudden fright or horror:They stood aghast at the sight of the plane crashing.
  • Gmc causative *gaistjan; see ghost
  • Middle English agast frightened, past participle of agasten, equivalent. to a- a-3 + gasten, Old English gǣstan to frighten, earlier *gāstjan 1225–75

Collins Concise English Dictionary © HarperCollins Publishers::
aghast /əˈɡɑːst/ adj
  1. (postpositive) overcome with amazement or horror
Etymology: 13th Century: agast, from Old English gæstan to frighten. The spelling with gh is on the model of ghastly
'aghast' also found in these entries (note: many are not synonyms or translations):

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