In a hushed or quiet manner; silently or with minimal sound.
Prefix 'a-' (meaning 'in a state of') combined with 'hush' (from Middle English, possibly imitating the sound of quietness), creating an archaic or poetic form meaning hushed.
This is an example of how English used to form adverbs and states more productively with the 'a-' prefix—you might encounter 'ahorse' or 'afoot' in old literature using the same pattern.
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