The Collaborative International Dictionary of English v.0.48:

Concert \Con*cert"\, v. t. [imp. & p. p. Concerted; p. pr. &
   vb. n. Concerting.] [F. concerter, It. concertare,
   conertare, prob. from L. consertus, p. p. of conserere to
   join together; con- + serere to join together, influenced by
   concertare to contend; con- + centare to strive; properly, to
   try to decide; fr. cernere to distinguish. See Series, and
   cf. Concern.]
   1. To plan together; to settle or adjust by conference,
      agreement, or consultation.
      [1913 Webster]

            It was concerted to begin the siege in March. --Bp.
                                                  Burnet.
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   2. To plan; to devise; to arrange.
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            A commander had more trouble to concert his defense
            before the people than to plan . . . the campaign.
                                                  --Burke.
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The Collaborative International Dictionary of English v.0.48:

Concerted \Con*cert"ed\, a.
   Mutually contrived or planned; agreed on; as, concerted
   schemes, signals.
   [1913 Webster]

   Concerted piece (Mus.), a composition in parts for several
      voices or instrument, as a trio, a quartet, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

concerted
    adj 1: involving the joint activity of two or more; "concerted
           action"; "the conjunct influence of fire and strong
           wind"; "the conjunctive focus of political opposition";
           "a cooperative effort"; "a united effort"; "joint
           military activities" [syn: concerted, conjunct,
           conjunctive, cooperative]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "concerted":
   accompanying, accordant, agreeing, associate, associated,
   at one with, coacting, coactive, coadjutant, coadjuvant, coadunate,
   coefficient, coincident, collaborative, collective, collectivist,
   collectivistic, collusive, combined, combining, commensal, common,
   communal, communalist, communalistic, communist, communistic,
   communitarian, concomitant, concordant, concurrent, concurring,
   conjoint, conniving, consilient, conspiratorial, cooperant,
   cooperating, cooperative, coordinate, coworking, ecumenic, fellow,
   harmonious, harmonized, joint, meeting, mutual, noncompetitive,
   parasitic, reciprocal, saprophytic, symbiotic, synchronous,
   synergetic, synergic, synergistic, uncompetitive, united,
   uniting