to make something dull or to cause something to lose its brightness, sharpness, or interest.
From Middle English be- (causative prefix) + dull (from Old Norse dulr or Old English origin, meaning 'slow to understand'). The prefix transforms the adjective dull into a verb meaning to cause dullness.
Even though we don't use 'bedull' anymore, we still do this with modern words—we 'brighten' something (to make bright) and 'darken' something (to make dark), showing how the English language recycles the same pattern.
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