region in northeastern Germany, traditionally said to be ultimately from Slavic, but perhaps German and meaning literally "burned fortress," or else from a Celtic proper name. In reference to a kind of ornamental button with loops, worn on the front of men's coats, by 1753, probably from Prussian military uniforms; later extended to ornamental buttons on women's dress (1873).

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Definitions of Brandenburg from WordNet

Brandenburg (n.)
the territory of an Elector (of the Holy Roman Empire) that expanded to become the kingdom of Prussia in 1701;