To trim or decorate something thoroughly, or to make very neat and orderly in appearance.
From 'be-' plus 'trim,' from Old Frisian 'trimen' meaning to make fit or proper. The combination suggests elaborate or thorough decoration.
The word 'trim' can mean both to cut down and to decorate—two opposite meanings that have somehow coexisted since medieval times, making 'betrim' wonderfully ambiguous.
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