Commonwealth BrE AmE noun
1 . [the] ( also British Commonwealth especially old use ), ˌCommonwealth of ˈNations formal an organization of about 50 independent countries, most of which were formerly part of the British Empire, established in order to encourage trade and friendly relations among its members. The British Queen is the head of the Commonwealth, and there is a meeting each year for all its heads of government.
2 . [countable] the official title of
a) some states of the US, for example Virginia and Kentucky,
b) some countries that are officially connected with the US, especially Puerto Rico, and
c) some countries made up of a group of states, such as Australia
3 . the Commonwealth England during the period 1649–60, when there was no king or queen and the country was ruled by Oliver Cromwell.