The Collaborative International Dictionary of English v.0.48:

coupled \coupled\ adj.
   1. joined together especially in a pair or pairs.

   Syn: conjugate, conjugated.
        [WordNet 1.5]

   2. connected by a physical link, as railway cars or trailer
      trucks. Opposite of unconnected or unlinked

   Syn: joined, linked.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Couple \Cou"ple\, v. t. [imp. & p. p. Coupled (k[u^]p"'ld); p.
   pr. & vb. n. Coupling (k[u^]p"l[i^]ng).] [F. coupler, fr.
   L. copulare. See Couple, n., and cf. Copulate, Cobble,
   v.]
   [1913 Webster]
   1. To link or tie, as one thing to another; to connect or
      fasten together; to join.
      [1913 Webster]

            Huntsman, I charge thee, tender well my hounds, . .
            .
            And couple Clowder with the deep-mouthed brach.
                                                  --Shak.
      [1913 Webster]

   2. To join in wedlock; to marry. [Colloq.]
      [1913 Webster]

            A parson who couples all our beggars. --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coupled
    adj 1: joined together especially in a pair or pairs [syn:
           conjugate, conjugated, coupled]
    2: connected by a link, as railway cars or trailer trucks [syn:
       coupled, joined, linked]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "coupled":
   accessory, accompanying, affiliate, affiliated, allied, assembled,
   associate, associated, attendant, attending, banded together,
   biconjugate, bigeminate, bijugate, bound, bracketed, cabalistic,
   coincident, collateral, collected, combined, concomitant,
   concurrent, confederate, confederated, conjoined, conjoint,
   conjugate, conjugated, connected, conspiratorial, copulate,
   corporate, correlated, correlative, enleagued, federate, federated,
   fellow, gathered, hand-in-glove, hand-in-hand, implicated,
   in cahoots, in league, in partnership, in with, incorporated,
   integrated, interlinked, interlocked, interrelated, intimate,
   involved, joined, joint, knotted, leagued, linked, married,
   matched, mated, merged, mutual, of that ilk, of that kind, one,
   paired, parallel, partnered, partners with, related, simultaneous,
   spliced, teamed, tied, twin, twinned, undivided, united,
   unseparated, wed, wedded, yoked