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c.1300, "the husk of wheat, barley, etc., separated from the flour after grinding," from Old French bren "bran, scurf, scales, feces" (12c., Modern French bran), perhaps connected with Gaulish *brenno- "manure," or with burn (v.). The word also was used 16c. in English for "dandruff flakes."
The outer layers of a cereal grain such as wheat, approximately 20 percent of which is indigestible cellulose, used as a source of dietary fiber.