nationalism UK /ˈnæʃənəlɪz(ə)m/US /ˈnæʃ(ə)nəˌlɪzəm/ noun3 •A more extreme form of patriotism; the idea of a more extreme support for one's country, people or culture.Communists, socialists, and Islamists are against nationalism. •Support for the creation of a sovereign nation (which does not currently exist). •(UK, Ireland) Support for the union of Northern Ireland and the Republic of Ireland. formsnationalisms