federalist

Short definition from Wiktionary

Noun

1. 1
   Advocate of federalism.
2. 2
   Supporter of the view that the province of Québec should remain within the Canadian federal system; an opponent of Québec‐based separatism or sovereigns.
3. 3
   A covenantalist.
4. 4
   A member of the Federalist Party, an 18th- and 19th-century conservative, liberal US political party which was one of two major parties under the First Party System.

Adjective

1. 1
   Of or relating to federalism, or its advocates.