Through something completely; all the way through.
From Old English 'athurh' or 'athuruh,' combining the prefix 'a-' with 'through.' This archaic form emphasizes the completion of passage from one side to another.
Old English loved these 'a-' prefixed words to emphasize motion or completion—'athrough' meant truly going all the way through, which is why modern English eventually simplified to just 'through.'
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