In or to a state of being stored or kept in reserve.
From the prefix a- (in a state of) plus store. This archaic formation reflects Middle English patterns of creating adverbs by prefixing a- to nouns, meaning 'in a state of' or 'in the manner of.'
Medieval merchants would say goods are 'astore' the way we'd say 'in storage'—it's a beautiful example of how a- changed from a productive prefix to a relic we only see in frozen phrases like 'asleep.'
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