riding: [11] Until 1974 Yorkshire was divided for administrative purposes into three ridings. The word has no connection with ride. It means etymologically ‘third part’. It was borrowed from Old Norse thrithjungr ‘third part’, a derivative of thrithi ‘third’. Its original English form was *thrithing, later thriding or triding, and it eventually lost its initial t through assimilation into the t of the preceding east and west. => three
