Word for the name part of a country name

geographical name, place name, (official) short name, short form name, common name, or alternative name.

Czech Republic, Wiki

Following the dissolution of Czechoslovakia at the end of 1992, the Czech part of the former nation found itself without a common single-word geographical name in English. The name Czechia /ˈtʃɛkiə/ was recommended by the Czech Ministry of Foreign Affairs (minister Josef Zieleniec). In a memorandum to all Czech embassies and diplomatic missions in 1993, the full name "Czech Republic" was recommended for use only in official documents and titles of official institutions.

The geographical name still has not reached general recognition, but its usage is increasing. Czech president Miloš Zeman uses the name Czechia in his official speeches. Czechia was approved by the Czech government on 2 May 2016 as the Czech Republic's official short name and was published in the United Nations UNTERM and UNGEGN country name databases on 5 July 2016. Czechia appears on some U.S. government web pages alongside Czech Republic, and Czechia is included in the ISO 3166 country codes list. In languages such as German (Tschechien), Danish (Tjekkiet) and Swedish (Tjeckien), the short-name has been in common use for many years. In January 2017 Czechia replaced Czech Republic on Google Maps.

The U.S. Board on Geographic Names is a Federal body created in 1890 and established in its present form by Public Law in 1947 to maintain uniform geographic name usage throughout the Federal Government. The Board comprises representatives of Federal agencies concerned with geographic information, population, ecology, and management of public lands. Sharing its responsibilities with the Secretary of the Interior, the Board promulgates official geographic feature names with locative attributes as well as principles, policies, and procedures governing the use of domestic names, foreign names, Antarctic names, and undersea feature names. [...]

The Board gradually expanded its interests to include foreign names and other areas of interest to the United States, a process that accelerated during World War II. In 1947, the Board was recreated by Congress in Public_Law_80-242 . The usefulness of standardizing (not regulating) geographic names has been proven time and again, and today more than 50 nations have some type of national names authority. The United Nations stated that "the best method to achieve international standardization is through strong programs of national standardization." Numerous nations established policies relevant to toponomy (the study of names) in their respective countries.

The GEOnet Names Server (GNS) provides access to the National Geospatial-Intelligence Agency's (NGA) and the U.S. Board on Geographic Names's (BGN) database of geographic feature names and locations for locations outside the United States. The database is the official repository of foreign place-name decisions approved by the US BGN. Approximately 20,000 of the database's features are updated monthly. The database never removes an entry, "except in cases of obvious duplication".