An archaic or obsolete verb meaning to furnish or provide with something, or to be associated with something.
From Old English 'be-' (causative/intensive prefix) combined with 'with,' which originally meant 'against' or 'alongside.' The 'be-' prefix transforms 'with' into a verb form, though this particular usage is now extinct in modern English. It represents one of many forgotten verb constructions from Middle English.
Most words starting with 'be-' that we've forgotten about show us how productive that prefix was in English—people could attach it to almost any word to create new verbs. 'Bewith' is basically a linguistic fossil, preserved only in old texts and showing us that English speakers were much more creative with word formation than we are today.
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