to assign (money, a grant, fund, etc) to one particular purpose, so as to restrict its useto ring-fence a financial allowance
to oblige (a person or organization) to use money for a particular purposeto ring-fence a local authority

noun ring fence

an agreement, contract, etc, in which the use of money is restricted to a particular purpose
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

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