constituent country

Constituent countries is a phrase used, often by official institutions, in contexts in which a number of countries make up a larger entity or grouping, concerning these countries; thus the OECD has used the phrase in reference to the parts of former Yugoslavia; the Soviet Union referring to the Soviet republics; and European institutions such as the Council of Europe frequently used the expression in reference to the European Union countries. It is not a term of art and has no defined legal meaning; 'constituent' is simply an adjective, and the phrase has no clear meaning outside a context from which the entity or grouping of which the countries in question are constituents or components can be understood.
See more at Wikipedia.org...