In a flushed state; blushing or with a reddened face, or abundant and flowing.
From 'a-' (in the state of) + 'flush,' where 'flush' comes from Middle English and possibly imitative in origin, meaning to flow or blush suddenly.
Medieval writers could say 'her cheeks were aflush' to create a poetic state-of-being that modern English separates into 'she was flushed'—we traded beautiful prefixes for simpler grammar.
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