The quality or state of being federal; the characteristic or essence of federalism in a system or organization.
From federal plus the suffix -ness (meaning quality or state), creating a noun that describes the abstract quality of being organized federally.
Federalness is such a technical, rare word that it barely appears in English, probably because 'federalism' does the job better—it's a good example of how English avoids creating words we don't really need.
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