The Collaborative International Dictionary of English v.0.48:

Confederate \Con*fed"er*ate\, v. t. [imp. & p. p.
   Confederated; p. pr. & vb. n. Confederating.]
   To unite in a league or confederacy; to ally.
   [1913 Webster]

         With these the Piercies them confederate. --Daniel.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Confederate \Con*fed"er*ate\, v. i.
   To unite in a league; to join in a mutual contract or
   covenant; to band together.
   [1913 Webster]

         By words men . . . covenant and confederate. --South.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Confederate \Con*fed"er*ate\, a. [L. confoederatus, p. p. of
   confoederare to join by a league; con- + foederare to
   establish by treaty or league, fr. foedus league, compact.
   See Federal.]
   1. United in a league; allied by treaty; engaged in a
      confederacy; banded together; allied.
      [1913 Webster]

            All the swords
            In Italy, and her confederate arms,
            Could not have made this peace.       --Shak.
      [1913 Webster]

   2. (Amer. Hist.) Of or pertaining to the government of the
      eleven Southern States of the United States which
      (1860-1865) attempted to establish an independent nation
      styled the Confederate States of America; as, the
      Confederate congress; Confederate money.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Confederate \Con*fed"er*ate\, n.
   1. One who is united with others in a league; a person or a
      nation engaged in a confederacy; an ally; also, an
      accomplice in a bad sense.
      [1913 Webster]

            He found some of his confederates in gaol.
                                                  --Macaulay.
      [1913 Webster]

   2. (Amer. Hist.) A name designating an adherent to the cause
      of the States which attempted to withdraw from the Union
      (1860-1865).
      [1913 Webster]

WordNet (r) 3.0 (2006):

Confederate
    adj 1: of or having to do with the southern Confederacy during
           the American Civil War; "Confederate soldiers"
    2: united in a confederacy or league [syn: allied,
       confederate, confederative]
    n 1: a supporter of the Confederate States of America
    2: someone who assists in a plot [syn: confederate,
       collaborator, henchman, partner in crime]
    3: a person who joins with another in carrying out some plan
       (especially an unethical or illegal plan) [syn: accomplice,
       confederate]
    v 1: form a group or unite; "The groups banded together" [syn:
         band together, confederate]
    2: form a confederation with; of nations

Moby Thesaurus II by Grady Ward, 1.0:

145 Moby Thesaurus words for "confederate":
   abettor, accessory, accompany, accomplice, accomplice in crime,
   act in concert, act together, adjunct, affiliate, affiliated,
   allied, ally, amalgamate, associate, associate with, associated,
   assort with, attend, band, band together, be in cahoots,
   be in league, bedfellow, brother, brother-in-arms, bunch, bunch up,
   cabal, cabalistic, cement a union, centralize, club, club together,
   coact, coadjutor, coalesce, coconspirator, cohort, collaborate,
   collaborator, colleague, collude, combine, come together,
   companion, compatriot, compeer, comrade, concert, concord, concur,
   confederated, confrere, consociate, consolidate, consort,
   consort with, conspirator, conspiratorial, conspire, cooperate,
   corporate, couple, couple with, coupled, crony, do business with,
   enleagued, federalize, federate, federated, fellow,
   fellow conspirator, fellow member, fellow traveler, flock together,
   fuse, gang, gang up, get heads together, get together,
   go along with, go in partners, go in partnership, go partners,
   go with, hang around with, hang together, harmonize, herd together,
   hold together, hook up, hook up with, in cahoots, in league,
   in partnership, in with, join, join forces, join fortunes with,
   join in, join together, join up with, join with, keep company with,
   keep together, league, league together, leagued, make common cause,
   married, marry, merge, organize, pair, pair off, paired, partner,
   partners with, play ball, pull together, put heads together,
   reciprocate, run with, socius criminis, stand together,
   stand up with, team up, team up with, team with, teamed,
   throw in together, throw in with, tie in, tie in with, tie up,
   tie up with, unionize, unite, unite efforts, unite with, wait on,
   wed, wedded, work together