to decorate something with frills; to add ornamental ruffles or fancy trimmings to fabric or a garment.
From be- (thorough/around) + frill (a decorative ruffle), with the 'be-' prefix intensifying the action. Used since the 1600s in fashion and sewing contexts.
The be- prefix is so productively English that people just keep creating new ones—befrill probably never appears in dictionaries, but a Victorian seamstress would instantly understand it as 'to add frills all over.'
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