On or as if on a wheel; in a spinning or rotating motion.
From 'a-' (in a state of) plus 'wheel.' This follows the Middle English pattern of forming descriptive adverbs by prefixing 'a-' to nouns or verbs to create vivid motion descriptions.
The 'a-' prefix was extremely productive in Middle and Early Modern English for creating dynamic descriptions of motion and position—like 'afoot' (on foot) or 'afloat' (on water)—though most have faded from use.
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