An archaic or poetic form meaning downward or down; rarely used in modern English.
From Old English 'of dune' or 'a-down,' with 'a-' (on, at) + 'down.' This is a Middle English adverbial form that became obsolete.
Medieval and Renaissance poets loved 'adown'—it appears in Spenser and Milton—because it created a different rhythm than simple 'down,' showing how older English had more options for poetic variation.
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