To overcome or gain mastery over something; to master (archaic or dialectal).
From 'a-' (to) + 'master,' creating a verb meaning to gain master-like control. This formation follows Middle English patterns of adding 'a-' to nouns to create verbs.
Amaister shows how English used to be more flexible—you could just add 'a-' to nearly any noun and make a verb, like medieval speakers were improvising their language on the fly, and most of those combinations died out when spelling got standardized.
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