The council chosen by the sovereign to administer public affairs. It consists of the Royal Family, the two Primates, the Bishop of London, the great officers of State, the Lord Chancellor and Judges of the Courts of Equity, the Chief Justices of the Courts of Common Law, the Judge Advocate, some of the Pusine Judges, the Speaker of the House of Commons, the Ambassadors, Governors of Colonies, Commander-in-Chief, Master-General of the Ordnance, First Lord of the Admiralty, Vice-President of the Board of Trade, Paymaster of the Forces, President of the Poor-law Board, etc. etc.; a committee of which forms the Cabinet or Ministry. The number of neither the Privy Council nor Cabinet is fixed, but the latter generally includes about fifteen or sixteen gentlemen specially qualified to advise on different departments of state business. Much of the business of the Privy Council is performed by Boards or subdivisions, as the Board of Trade, the Board of Quarantine, the Committee of Council on Education, etc.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Privy Council from Infoplease: