Entry 1 sense Webster, 1913 Federalism /fĕd'-ẽr-əl-ĭzˌ-əm/ · Fed·er·al·ism · IPA /fˈɛdərəlˌɪzəm/ 01 n. The principles of Federalists or of federal union. 1. The principles of Federalists or of federal union.