The Collaborative International Dictionary of English v.0.48:

Confederacy \Con*fed"er*a*cy\, n. (Amer. Hist.)
   With the, the Confederate States of America.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Confederacy \Con*fed"er*a*cy\, n.; pl. Confederacies. [From
   Confederate, a.]
   1. A league or compact between two or more persons, bodies of
      men, or states, for mutual support or common action;
      alliance.
      [1913 Webster]

            The friendships of the world are oft
            Confederacies in vice or leagues of pleasure.
                                                  --Addison.
      [1913 Webster]

            He hath heard of our confederacy.     --Shak.
      [1913 Webster]

            Virginia promoted a confederacy.      --Bancroft.
      [1913 Webster]

   2. The persons, bodies, states, or nations united by a
      league; a confederation.
      [1913 Webster]

            The Grecian common wealth, . . . the most heroic
            confederacy that ever existed.        --Harris.
      [1913 Webster]

            Virgil has a whole confederacy against him.
                                                  --Dryden.
      [1913 Webster]

   3. (Law) A combination of two or more persons to commit an
      unlawful act, or to do a lawful act by unlawful means. See
      Conspiracy.

   Syn: League; compact; alliance; association; union;
        combination; confederation.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "confederacy":
   Anschluss, Bund, Rochdale cooperative, addition, affiliation,
   agglomeration, aggregation, agreement, alignment, alliance,
   amalgamation, anschluss, artifice, assemblage, assimilation,
   association, axis, band, blend, blending, bloc, body, cabal,
   cahoots, cartel, centralization, coadunation, coalescence,
   coalition, colleagueship, college, collegialism, collegiality,
   collusion, combination, combine, combo, common market, complicity,
   complot, composition, comradeship, confederation, confraternity,
   congeries, conglomeration, conjugation, conjunction, connivance,
   consolidation, conspiracy, consumer cooperative, contrivance,
   contriving, cooperative, cooperative society, copartnership,
   copartnery, corps, council, counterplot, covin, credit union,
   customs union, deep-laid plot, economic community, ecumenism,
   embodiment, encompassment, engineering, enosis, federalization,
   federation, fellowship, finagling, finesse, frame-up, fraternalism,
   fraternity, fraternization, free trade area, freemasonry, fusion,
   game, gang, group, grouping, hookup, inclusion, incorporation,
   integration, intrigue, junction, junta, league, little game,
   machination, machine, maneuvering, manipulation, marriage, meld,
   melding, merger, mob, package, package deal, partnership, plot,
   plotting, political machine, rigging, ring, scheme, schemery,
   scheming, society, sodality, solidification, sorority, stratagem,
   syncretism, syndication, syneresis, synthesis, tie-in, tie-up,
   trick, underplot, unification, union, web of intrigue, wedding,
   wire-pulling