Third person singular present tense of 'gast,' an archaic verb meaning to frighten, terrify, or shock someone.
From Old English gæstan or gasten. Related to ghost and aghast. The word became archaic as modern English adopted 'frighten' and 'terrify,' though 'aghast' preserves its meaning.
The word 'aghast' literally comes from 'gast'—when you're aghast, you're 'a-gasted' or gasped with fear, making it one of English's most poetic surviving remnants of an older vocabulary.
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