In an extremely wicked, cruel, or brutal manner; in a shockingly bad way.
From Latin 'atrocis' (cruel, savage, literally 'blackened') derived from 'ater' (black, dark). The adverb form adds '-ly' to 'atrocious,' evolving from descriptions of dark deeds to any extremely awful behavior or quality.
The word 'atrocious' literally meant 'blackened' in Latin—people thought of terrible crimes as morally dark, so they used the word for black to describe black-hearted villains!
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