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county borough

noun

(in England and Wales from 1888 to 1974 and in Wales from 1996) a borough administered independently of any higher tier of local government
(in the Republic of Ireland) any of the four largest boroughs, governed independently of the administrative county around it by an elected council that constitutes an all-purpose authority
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012