the formation of a political unity, with a central government, by a number of separate states, each of which retains control of its own internal affairs.
3.
a league or confederacy.
4.
a federated body formed by a number of nations, states, societies, unions, etc., each retaining control of its own internal affairs.
Origin: 1715–25; < Late Latinfoederātiōn- (stem of foederātiō) a leaguing. See federate, -ion
Federation is first attested 1721, from L.L. foederationem, from L. foederare "league together," from foedus "covenant, league" (gen. foederis); see federal.