The Collaborative International Dictionary of English v.0.48:

League \League\, v. i. [imp. & p. p. Leagued; p. pr. & vb. n.
   Leaguing.] [Cf. F. se liguer. See 2d League.]
   To unite in a league or confederacy; to combine for mutual
   support; to confederate. --South.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "leagued":
   accumulated, affiliate, affiliated, agglomerate, aggregate, allied,
   amassed, assembled, associate, associated, banded together, bound,
   bracketed, bunched, bundled, cabalistic, clumped, clustered,
   collected, combined, confederate, confederated, conglomerate,
   congregate, congregated, conjoined, connected, conspiratorial,
   copulate, corporate, coupled, cumulate, enleagued, fascicled,
   fasciculated, federate, federated, gathered, glomerate,
   hand-in-glove, hand-in-hand, heaped, in cahoots, in league,
   in partnership, in session, in with, incorporated, integrated,
   intimate, joined, joint, knotted, linked, lumped, married, massed,
   matched, mated, meeting, merged, packaged, paired, partners with,
   piled, spliced, stacked, teamed, tied, undivided, united,
   unseparated, wed, wedded, wrapped up, yoked