Pertaining to a league, covenant, or contract; derived from a covenant between parties, particularly between nations.Confederated; founded on an alliance by confederation or compact for mutual support: as, the federal diet of the old German empire.Pertaining to a union of states in some essential degree constituted by and deriving its power from the people of all, considered as an entirety, and not solely by and from each of the states separately: as, a federal government, such as the governments of the United States. Switzerland, and some of the Spanish-American republics.Favorable to federation; supporting the principle of a union of states under a common government; specifically, in the United States, relating to, or adhering to, the support of the Federal Constitution.In the American civil war, pertaining to or supporting the Union or federal government.n. A supporter of federation; one devoted to a union of states in a national government or to its preservation; a unionist. Specificallyn. In the American civil war, a Unionist; particularly, a Union soldier: opposed to Confederate.