central bank

A central bank, reserve bank or monetary authority, is an entity responsible for the monetary policy of its country or of a group of member states. Its primary responsibility is to maintain the stability of the national currency and money supply, but more active duties include controlling subsidized-loan interest rates, and acting as a "bailout" lender of last resort to the banking sector during times of financial crisis (private banks often being integral to the national financial system). It may also have supervisory powers, to ensure that banks and other financial institutions do not behave recklessly or fraudulently.
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Noun
1. a government monetary authority that issues currency and regulates the supply of credit and holds the reserves of other banks and sells new issues of securities for the government
(hypernym) financial institution, financial organization, financial organisation
(hyponym) European Central Bank

A country's main bank whose responsibilities include the issue of currency, the administration of monetary policy, open market operations, and engaging in transactions designed to facilitate healthy business interactions. See: Federal Reserve System.

the generic name given to a country's primary monetary authority, such as the Bank of England in the UK (they set interest rates) or the Federal Reserve System in the U.S.