Central bank is a financial institution which controls and supervises the entire monetary system of a country while Commercial bank may be defined as a financial institution which carries out retail banking services, set up for keeping and lending money to people, owned by organisations, individual or governments, for the purpose of making profits.
The United Nations or UN, also called the United Nations Organization (UNO), is the largest and most important international organization on the planet. Most of the world's recognized nations ascribe to it.