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.
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            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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