To make white; to whiten or bleach something completely.
From 'be-' plus 'white' (Old English 'hwīt'). Following the same pattern as beweary and bewater—turning an adjective into an action verb.
The existence of both 'bewhite' and 'bewhiten' (the variant below) shows how flexible English verb-making was—adding '-en' to a 'be-' verb created nuanced alternatives.
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